High solids content slurries, systems and methods

ABSTRACT

High solids content slurry, systems and methods. The slurry comprises a carrier fluid and a solids mixture of first, second, third and fourth particle size distribution (PSD) modes wherein the first PSD mode is at least three times larger than the second PSD mode, which is larger than the third PSD mode, which is larger than the fourth PSD mode, and wherein at least one of the second and third PSD modes is less than 3 times larger than the respective third or fourth PSD mode. The method comprises forming the slurry, positioning a screen in a wellbore and circulating the slurry through the wellbore such that the solids mixture is deposited between the screen and the wellbore. The system comprises a pump to circulate the slurry, a workstring to position the screen and means for converting the slurry to a gravel pack.

CROSS REFERENCE TO RELATED APPLICATIONS

None. U.S. Pat. No. 7,789,146 and U.S. Pat. No. 7,784,541 are herebyincorporated herein by reference in their entireties.

BACKGROUND

The statements in this section merely provide background informationrelated to the present disclosure and may not constitute prior art.

Patent application publications US 2009/0025932 and US 2009/0025934 arehereby incorporated herein by reference in their entireties.

Gravel packs are placed in wellbores between a screen and a formationface and/or casing to prevent formation sand from flowing into thewellbore and to improve wellbore and near-wellbore conductivity. Theconductivity at the wellbore and near-wellbore is important because anydamage in these locations significantly increases the pressure drop offluid flow, thereby reducing the producibility or injectivity of thewell.

Further, current placement techniques for gravel packs, with or withoutsimultaneous hydraulic fracturing of the formation, can be a complexprocedure requiring several stages and the proper functioning of movingparts in a hostile wellbore environment. Accordingly, there is a demandfor further improvements in this area of technology.

SUMMARY

Some embodiments are unique procedures for creating a high solidfraction fluid. Other embodiments include unique systems, methods,systems and apparatus for low damage gravel packing. Furtherembodiments, forms, objects, features, advantages, aspects, and benefitsshall become apparent from the below description and drawings.

The current invention in various embodiments describes methods, slurriesand systems of gravel packing or frac-packing a well using slurries thatcontain a high fraction of solids. The solids comprise a plurality ofdifferent particle size distribution modes to increase the solid volumefraction in the slurry and the packed volume fraction in the gravel orfracture pack. In one embodiment, the solids mixture comprises aplurality of volume-average particle size distribution (PSD) modeswherein a first PSD mode comprises solids having a volume-averagedmedian size at least three times larger than the volume-average mediansize of a second PSD mode such that a packed volume fraction (PVF) ofthe solids mixture exceeds 0.75 or preferably exceeds 0.8. In anotherembodiment, the smaller PSD modes can be removed from the pack toincrease porosity and permeability for the flow of fluids through thepack.

In one embodiment, a method comprises combining a carrier fluid and asolids mixture to form a slurry, wherein the solids mixture comprises aplurality of volume-averaged particle size distribution (PSD) modes,wherein a first PSD mode comprises solids having a volume-average mediansize at least three times larger than the volume-average median size ofa second PSD mode such that a packed volume fraction (PVF) of the solidsmixture exceeds 0.75 or preferably exceeds 0.8, and wherein the solidsmixture comprises a degradable material and includes a reactive solid;circulating the slurry through a wellbore to form a pack of the solidsmixture having a PVF exceeding 0.75 or preferably exceeds 0.8 in one orboth of a fracture in a formation and an annulus between a screen andthe wellbore; degrading the degradable material in the pack to increaseporosity and permeability of the pack; and producing a reservoir fluidfrom the formation through the increased porosity pack.

In one embodiment, the degradable material can be dissolved by changingthe pH in the solids pack. For example, alumina trihydrate particles ata neutral pH are solubilized at a high as well as at a low pH. In otherembodiments, the degradable material is soluble in basic fluids, e.g.,the degradable material is selected from amphoteric oxides, esters,coated acids and combinations thereof; and the solids mixture canfurther include a base or a base precursor that is optionally sparinglysoluble and/or encapsulated, or the solids can be contacted with a basicaqueous solution.

In further embodiments, the degradable material is soluble in acidicfluids, e.g., the degradable material is selected from oxides andhydroxides of aluminum, zinc, tin, lead, boron, silicon and iron;carbonates, sulfates, oxides and hydroxides of calcium, magnesium andbarium; and combinations thereof; and the solids mixture can furtherinclude an acid or an acid precursor that is optionally sparinglysoluble and/or encapsulated, or the solids can be contacted with anacidic aqueous solution. In one embodiment, the acid precursor isselected from the group consisting of hydrolyzable esters, acidanhydrides, acid sulfonates, acid halides and combinations thereof.

In further embodiments, the degradable material can be an encapsulatedwater- or oil-soluble solid which can be removed from

the gravel or proppant pack by de-encapsulating the solid. Alternativelyor additionally the degradable material can be a water-soluble solid,and the carrier in the slurry can be either a saturated solution of thesoluble solid, e.g. salt solids and brine, or an invert emulsion whereinthe soluble solid is dispersed in the oil phase. The soluble solid canbe removed by contacting the pack with an undersaturated aqueous mediumand/or breaking the emulsion.

In another embodiment, a composition comprises the slurry used in themethod just described, i.e., a carrier fluid and a solids mixturecombined to form a flowable slurry, wherein the solids mixture comprisesa plurality of volume-averaged particle size distribution (PSD) modes,wherein a first PSD mode comprises solids having a volume-average mediansize at least three times larger than the volume-average median size ofa second PSD mode such that a packed volume fraction (PVF) of the solidsmixture exceeds 0.75, and wherein the solids mixture comprises adegradable material and includes a reactive solid.

In another embodiment, the invention addresses the issue of fluidleak-off from the multimodal slurry into the screen. Loss of fluid fromthe multimodal slurry can cause premature bridging, making it difficultto place the slurry in the annulus around the screen in the screen-firstplacement method, or to stab the screen into the multimodal slurry inthe slurry-first placement method. In one embodiment, the screen isplugged with a degradable fluid loss particle, which after gravelplacement and screen placement, is later removed by dissolution forexample to restore permeability of the screen element for production offluid from the formation. In an embodiment, the screen is contacted witha spacer fluid comprising the degradable fluid loss particles in advanceof contact of the screen with the gravel-containing slurry. In theadvance-spacer embodiment: the spacer can be pumped downhole into theannulus around the screen positioned downhole in the screen-firstmethod, followed by the slurry containing the gravel; or, in the case ofthe slurry-first embodiment, the slurry is placed in the wellbore,followed by the spacer placed above the gravel-containing slurry, andthen the screen is passed through the spacer before entering the slurry,whereby the screen is at least temporarily blocked with the fluid lossparticles to inhibit leak-off from the multimodal slurry into thescreen.

In an alternate embodiment, the multimodal slurry comprises abridge-forming composition to form a bridge on the screen when theslurry is placed in contact with the screen, whereby the screen is atleast temporarily blocked to inhibit leak-off from the multimodal slurryinto the screen.

In an embodiment, a method comprises: combining a carrier fluid and asolids mixture to form a slurry, wherein the solids mixture comprises aplurality of volume-averaged particle size distribution (PSD) modes suchthat a packed volume fraction (PVF) of the solids mixture exceeds 0.75or preferably exceeds 0.8; contacting a screen with a fluid comprisingleak-off control agent to form a bridge on the screen to inhibit fluidentry; positioning the screen in a wellbore and circulating the slurrythrough the wellbore in any order such that the solids mixture isdeposited between the screen and the wellbore; degrading the degradablematerial in the pack to increase porosity and permeability of the pack;removing the bridge from the screen; and producing a reservoir fluidfrom the formation through the increased porosity pack and the screen.

In an embodiment, the leak-off control fluid comprises a spacer fluidintroduced into the wellbore. In an embodiment, the slurry is circulatedthrough the wellbore before the screen is positioned in the wellbore,the spacer fluid is positioned in the wellbore above the slurry, and thescreen is passed through the spacer fluid in the wellbore and thenstabbed into the slurry. In an alternate embodiment, the screen ispositioned in the wellbore before the slurry is circulated into anannulus between the screen and the wellbore, and wherein the spacerfluid is circulated into the annulus ahead of the slurry. In anembodiment, the spacer fluid and slurry are sequentially pumped througha central flow passage to a bottom end of the screen and into theannulus.

In an embodiment, the slurry comprises the leak-off control agent andthe bridge is formed on the screen during the circulation of the slurry.In an embodiment, the solids mixture comprises at least three PSD modes,wherein a first amount of particulates have a first PSD, a second amountof particulates have a second PSD, and a third amount of particulateshave a third PSD, wherein the first PSD is from two or three to tentimes larger than the second PSD, and wherein the second PSD is largerthan the third PSD, preferably from 1.5 to ten times larger in oneembodiment, from three to ten or fifteen times larger in anotherembodiment, from about 1.5 to 4 times larger in an alternate embodiment,and from 1.5 to less than three times larger in a further embodiment. Inan alternate or additional embodiment, the solids mixture comprises thethree or more PSD modes to form the bridge on the screen.

In further embodiments, the carrier fluid may further comprise a fluidloss additive, such as, for example, latex dispersions, water solublepolymers, submicron particles, and particulates with different shapes,and/or a slurry stabilizer, such as, for example, nanoparticles,polymers that hydrate at high temperatures, and high aspect ratioparticles.

In another embodiment, the slurry placement may require that the slurrystay suspended for extended periods of time without settling so thatrheological characteristics are retained, for example, when thegravel-laden slurry is placed in an open hole followed by screen stab-inthere may be a delay of as much as 48 hours between slurry circulationinto the wellbore and screen stab-in while the slurry circulationworkstring is removed from the hole and the screen is tripped in. If thesolids settle prematurely, the high solids content slurry may lose itsfluid like properties and an excessive amount of force may be requiredto push the screen into the settled slurry. In an embodiment accordingto the present invention, a slurry comprises a solids mixture comprisinga plurality of PSD modes such that a PVF exceeds 0.75, preferablyexceeds 0.8; a carrier fluid in an amount to provide an SVF less thanthe PVF of the solids mixture; and a stability additive to inhibitsettling of the solids mixture. In another embodiment, a methodcomprises combining the carrier fluid, the solids mixture and thestability additive to form the slurry; circulating the slurry into awellbore to deposit the slurry downhole; terminating the slurrycirculation for a period of time, wherein the stability additiveinhibits settling of the solids mixture; and thereafter circulating thedeposited slurry in contact with a surface of a screen.

In embodiments, the stability additive comprises colloidal particlessuch as, for example, γ-alumina, MgO, γ-Fe2O3, and combinations thereof;hydratable polymer particles, e.g., polymer particles having a hydrationtemperature above 60° C. such as gellan gum; high aspect ratioparticles, e.g. an aspect ratio above 6, such as, for example, flakeswhich may be optionally degradable such as a polymer or copolymer oflactide and/or glycolide.

The present invention provides embodiments for placing the slurry in agravel packing operation. In various embodiments, a gravel packingscreen is placed in a wellbore and the slurry and/or the slurry solidsare placed in an annulus between the screen and the wellbore, in eitherorder. In one embodiment, the screen is initially placed in the wellbore“screen-first” and then the slurry is circulated down the tubing,through a packer and crossover port, and into the annular space aroundthe screens. In a further screen-first embodiment, the slurry deploymentcan include a “bottoms-up” method of pumping, which allows inembodiments for gravel packing and/or fracturing immediatelypost-drilling, for gravel packing-while cementing, for the inclusion ofchemical packers, for the use of large diameter screens and otheradditional variations. In another embodiment, a “stab-in” technique isused wherein the slurry is initially circulated into the wellbore, andthen the screen is positioned in the wellbore. In this embodiment, thescreen displaces the slurry from the central portion of the wellbore andthe slurry fills or remains in the screen-wellbore annulus.

In another embodiment, after the slurry is placed in the annulus of thescreen and the open/cased hole and/or in a fracture, all or at least aportion of the solid particles other than gravel in the fluid are flowedback to the surface leaving a permeable gravel pack in the annulus. Inthis embodiment, the method comprises forming a stable, flowable slurrycomprising a carrier fluid and a solids mixture, wherein the solidsmixture comprises a plurality of volume-averaged particle sizedistribution (PSD) modes such that a packed volume fraction (PVF)exceeding 0.75, preferably exceeding 0.8, and wherein the solids mixturecomprises at least a proppant PSD mode and a fines PSD mode. In anembodiment, the slurry is circulated through a wellbore to form aproppant pack from depositing the solids mixture in one or both of afracture in a formation and an annulus between a screen and thewellbore, the fines in the pack are contacted with a dispersant, andfluid is passed through the pack to remove fines.

Another embodiment is a system for effecting the fines flowback method.In this embodiment, a well bore is provided in fluid communication witha subterranean formation. In an embodiment, a gravel packing slurrycomprises a carrier fluid and a solids mixture, wherein the solidsmixture comprises a plurality of volume-averaged particle sizedistribution (PSD) modes such that a packed volume fraction (PVF)exceeding 0.75, preferably exceeding 0.8, wherein the solids mixturecomprises at least a proppant PSD mode and a fines PSD mode. A pump isadapted to circulate the slurry in the wellbore to deposit the solidsmixture and form a proppant pack in one or both of a fracture in theformation and an annulus between a screen and the formation. The systemcomprises a dispersant source effective to facilitate fines flowbackfrom the pack.

In one embodiment, a multi-PSD mode slurry comprises relatively largeproppant, e.g., of a type and size commonly used in gravel packing, andthe slurry has a composition to efficiently control leak-off into thescreen and/or the formation while facilitating removal of the smallerparticles after placement of the gravel. This slurry method and systemin an embodiment allows transport of gravel to the toe of the well at alow flow rate, without having to change the washpipe diameter to controlleak-off, and may also reduce the risk of fracturing in long horizontalswhere a high pump rate would otherwise be required to transport gravelusing conventional methods and systems. In one embodiment, a slurrycomprises a solids mixture in a carrier fluid. The solids mixture inthis embodiment comprises at least first, second, third and fourthvolume-averaged particle size distribution (PSD) modes such that apacked volume fraction (PVF) of the solids mixture is greater than 0.75,preferably greater than 0.80, wherein a solids volume fraction (SVF) ofthe slurry less than the PVF of the solids mixture, wherein the firstPSD mode is at least three times larger than the second PSD mode, thesecond PSD mode is larger than the third PSD mode, and the third PSDmode is larger than the fourth PSD mode, and wherein at least one of thesecond and third PSD modes is less than 3 times larger than therespective third or fourth PSD mode. In one embodiment, the solidsmixture further comprises a fifth PSD mode, wherein the fourth PSD modeis larger than the fifth PSD mode and preferably less than 3 timeslarger than the fifth PSD mode.

In embodiments where the smaller PSD modes are closer in size relativeto the next larger and/or smaller PSD modes, a relatively high solidspacking volume fraction can be obtained using a smaller proportion ofthe smaller PSD modes, and yet, surprisingly, fines flowback can befacilitated when it is desired to convert the high PVF pack into apermeable gravel pack and/or fracture pack.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a schematic diagram of a system for low damage gravel packing.

FIG. 2 is a schematic diagram of a device for depositing particulatesbetween an outer surface of a screen and a surface of a wellboreformation.

FIG. 3A is a schematic diagram of a device for depositing particulatesbetween an outer surface of a screen and a surface of a wellboreformation in a first position.

FIG. 3B is a schematic diagram of a device for depositing particulatesbetween an outer surface of a screen and a surface of a wellboreformation in a second position.

FIG. 4A is a schematic diagram of a device for depositing particulatesbetween an outer surface of a screen and a surface of a wellboreformation in a first position.

FIG. 4B is a schematic diagram of a device for depositing particulatesbetween an outer surface of a screen and a surface of a wellboreformation in a second position.

FIG. 4C is a schematic diagram of a device for depositing particulatesbetween an outer surface of a screen and a surface of a wellboreformation in a third position.

FIG. 5 is a schematic diagram of an embodiment of a device fordepositing particulates between an outer surface of a screen and awellbore formation using a bottoms up slurry deployment technique.

FIG. 6A is a schematic diagram of an embodiment of a device fordepositing particulates between an outer surface of a screen and awellbore formation using a bottoms up slurry deployment techniquewherein the slurry is pumped through the screen assembly via a washpipe.

FIG. 6B is a schematic diagram of the embodiment of FIG. 6A followingplacement of the slurry and setting of the packers.

FIG. 7 is a schematic diagram of an embodiment of a device similar tothat of FIG. 6 for depositing particulates in a fracture, as well asbetween an outer surface of a screen and a wellbore formation, using abottoms up slurry deployment technique wherein the slurry is pumpedthrough the screen assembly via a washpipe.

FIG. 8A is a transverse cross sectional schematic diagram of anembodiment of a device for depositing particulates between an outersurface of a screen and a wellbore formation using a bottoms up slurrydeployment technique wherein blocked screens are run in hole as a partof the final production run.

FIG. 8B is a perspective partially cutaway schematic diagram of thedevice of FIG. 8A following removal of the blocking for production.

FIG. 9 is a transverse cross sectional schematic diagram of an alternateembodiment of the device of FIGS. 8A-8B wherein the basepipe is blocked.

FIG. 10 is a transverse cross sectional schematic diagram of the deviceof FIG. 9 following removal of the blocking for production.

FIG. 11 is a longitudinal cross sectional schematic diagram of analternate embodiment of the devices of FIGS. 8A, 9 wherein inflowthrough the screens is blocked using a mechanical inflow control device.

FIG. 12 is a longitudinal cross sectional schematic diagram of thedevice of FIG. 11 following actuation of the mechanical inflow controldevice for production.

FIG. 13 is a schematic diagram of an embodiment of a device fordepositing particulates between an outer surface of a screen and awellbore formation using a bottoms up slurry deployment technique withchemical packers.

FIG. 14 is a schematic diagram of an embodiment of a device fordepositing particulates between an outer surface of a screen and awellbore formation using a bottoms up slurry deployment technique with adiversion port for chemical packers.

FIG. 15 is a schematic diagram of an embodiment of a device fordepositing particulates between an outer surface of a screen and awellbore formation using a bottoms up slurry deployment techniquewherein the screens are run during drilling.

FIG. 16 is an illustration of a carrier fluid combined with a first,second, and third amount of particles in a slurry.

FIG. 17 is an illustration of a carrier fluid combined with a first,second, and third amount of particles in a slurry.

FIG. 18 is a schematic flow diagram of operations for low damage gravelpacking.

FIG. 19A is a schematic flow diagram of a technique for low damagegravel packing using a screen-first procedure.

FIG. 19B is a schematic flow diagram of a technique for low damagegravel packing using a slurry-first procedure.

FIG. 20 is a schematic diagram of a stab-in embodiment wherein ascreen-bridging spacer fluid is placed on top of the multimodal slurryin the wellbore.

FIG. 21 is a schematic diagram of a screen-first embodiment wherein ascreen-bridging spacer fluid is circulated into the screen annulus aheadof the multimodal slurry.

FIG. 22 is a schematic diagram of the screen-first embodiment of FIG. 21wherein the multimodal slurry is placed in the annulus after leak-offcontrol additives from the spacer fluid have plugged or bridged thescreen elements to limit leak-off from the slurry.

FIG. 23 is a plot of syringe leak-off for a tetramodal slurry as afunction of the second largest particle size at different concentrationsof the second largest particle, according to an embodiment of theinvention as discussed in Example 13.

FIG. 24 is a plot of syringe leak-off for a tetramodal slurry as afunction of the third largest particle size, according to an embodimentof the invention as discussed in Example 13.

FIG. 25 illustrates a tetramodal particle packing model based on theDescartes circle theorem involving mutually tangent circles, accordingto an embodiment of the invention as discussed in Example 13.

DETAILED DESCRIPTION

At the outset, it should be noted that in the development of any suchactual embodiment, numerous implementation—specific decisions must bemade to achieve the developer's specific goals, such as compliance withsystem related and business related constraints, which will vary fromone implementation to another. Moreover, it will be appreciated thatsuch a development effort might be complex and time consuming but wouldnevertheless be a routine undertaking for those of ordinary skill in theart having the benefit of this disclosure. In addition, the compositionused/disclosed herein can also comprise some components other than thosecited. In the summary and this detailed description, each numericalvalue should be read once as modified by the term “about” (unlessalready expressly so modified), and then read again as not so modifiedunless otherwise indicated in context. Also, in the summary and thisdetailed description, it should be understood that a concentration rangelisted or described as being useful, suitable, or the like, is intendedthat any and every concentration within the range, including the endpoints, is to be considered as having been stated. For example, “a rangeof from 1 to 10” is to be read as indicating each and every possiblenumber along the continuum between about 1 and about 10. Thus, even ifspecific data points within the range, or even no data points within therange, are explicitly identified or refer to only a few specific, it isto be understood that inventors appreciate and understand that any andall data points within the range are to be considered to have beenspecified, and that inventors possessed knowledge of the entire rangeand all points within the range.

As used in the specification and claims, “near” is inclusive of “at.”

As used herein, the terms “bimodal” and “multimodal” with respect toparticle size or other variable distribution have their standardstatistical meanings. In statistics, a bimodal distribution is acontinuous probability distribution with two different modes. A mixtureis considered to be multimodal if it has two or more modes. These modesappear as distinct peaks (local maxima) in the probability densityfunction. A bimodal distribution can arise as a mixture of two differentunimodal distributions, i.e., distributions having only one mode. Forexample, a bimodally distributed particle size can be defined as PSD₁with probability α or PSD₂ with probability (1−α), where PSD₁ and PSD₂are different unimodal particle sizes and 0<α<1 is a mixturecoefficient. A mixture of two unimodal distributions with differingmeans is not necessarily bimodal; however, a mixture of two normaldistributions with similar variability is considered to be bimodal iftheir respective means differ by more than the sum of their respectivestandard deviations.

As used herein, the term “bridge” refers to the occlusion of passages,e.g., the openings in a screen element, to inhibit fluid flow. Thus, theterm would not apply to the formation of a filter cake on a screensurface that does not significantly inhibit fluid flow through thescreen. Conversely, “removing a bridge” and similar terms refer to theremoval of the occlusions to restore fluid flow and also includemodification of the structure of the bridge to an extent sufficient torestore fluid flow, e.g., removing a bridge can involve forming holesthrough the filter cake and/or removing smaller particles from a filtercake on a screen element to establish permeability, without physicallyremoving the filter cake matrix.

The term “aspect ratio” as applied herein to particles is understood asbeing the ratio of the longest dimension of the particle to the shortestdimension. A sphere or a cube has an aspect ratio of 1, for example. Anaspect ratio greater than one means the particle is elongated in onedirection. Sometimes the aspect ratio is given as less than one, meaningthat the longest dimension is used in the denominator rather than thenumerator, but is understood in the art to be equivalent to itsreciprocal where the aspect ratio is greater than one, e.g., an aspectratios of 0.5 and 2.0 are equivalent, as are 0.25 and 4.0.

FIG. 1 is a schematic diagram of one embodiment of a system 100 for lowdamage gravel packing. In certain embodiments, the system 100 includes awell 102 drilled through an overburden 104 and a formation of interest106. The formation of interest 106 may include a hydrocarbon producingformation, a water producing formation, a target formation for injectionof a fluid, or other formation of interest known in the art. In certainembodiments, the well 102 has a wellhead 108, and a casing 110 coveringat least a portion of the wellbore. In the illustration of FIG. 1, thewellbore through the formation of interest 106 is an “open hole”completion in a vertical well. Other types of completions arecontemplated in the present application, including without limitation: acased completion, multiple zone completions, and/or a horizontal well orwell segment. The casing 110 may include a cement layer (not shown)between the casing 110 and the formation(s) (104, 106). Various otherfeatures of the system 100 that are known in the art are not shown ordescribed herein to avoid obscuring aspects of the present application.

The system 100 further includes, in certain embodiments, a screen 112disposed in the wellbore. The screen 112 may include slots or holessized to prevent the flow of particles from the formation of interest106 into the well 102 or to the surface during treatment flowback orproduction of the well 102. In certain embodiments, the system 100includes a gravel pack 114 deposited between the screen 112 and theformation of interest 106. The gravel of the gravel pack 114 may bedeposited as a portion of a slurry 116 comprising particles (118, 120)and a carrier fluid 122 as described in more detail below.

In certain embodiments, the slurry 116 is pumped through the well 102 todeposit the first amount of particulates 118 and the second amount ofparticulates 120 between the screen 112 and the formation of interest106. The slurry 116 may be pumped outside the screen 112 into theformation of interest 106 until a screen-out occurs (i.e. theparticulates 118, 120 build up to the point where the pressure dropacross the gravel pack 114 prevents further pumping), the slurry 116 maybe circulated through the well 102 such that the slurry 116 passes fromoutside the screen 112 to inside the screen 112, thereby depositing theparticulates 118, 120 between the screen 112 and the formation ofinterest 106 and circulating the carrier fluid 122 to the surface. Incertain embodiments, the slurry 116 may be placed in the wellbore 102and the screen 112 lowered into the already-placed slurry 116 such thatthe particulates 118, 120 in the slurry 116 are thereby depositedbetween the screen 112 and the formation of interest 106.

In certain embodiments, the system 100 includes various devices tocontrol mixing and pumping the slurry 116. In one exemplary embodiment,the system 100 includes at least one fluid tank 124 which contains thecarrier fluid 122 and/or a base fluid utilized in the creation of thecarrier fluid 122. The exemplary embodiment further includes a gravelcarrier 126 which, in one embodiment, provides the first amount ofparticulates 118 to a blending device 128. The blending device 128prepares the final slurry 116, for example mixing the gravel fluid 122and adding the first amount of particulates 118 from the gravel carrier126, and further adding any additives, the second amount of particulates120 and/or third or any other amount of particulates. In certainembodiments, more than one particulate amount may be blended and addedby the gravel carrier 126 or other device. The blending device 128further provides the slurry 116 to a pumping device 130 that providespressurized slurry 116 to the wellhead 108. Other equipmentconfigurations are understood in the art and contemplated herein. Forexample, and without limitation, the system 100 may include a coiledtubing unit (not shown) in place of one or more pieces of equipmentand/or tubing 132 connected to the screen 112.

FIG. 2 is a schematic diagram of one embodiment of a device fordepositing particulates 118, 120 between an outer surface of a screen112 and a surface of a formation of interest 106. The slurry 116 ispumped through a crossover tool 202 from a tubing 132 to the screenannulus 203. The carrier fluid 122 of the slurry 116 recirculatesthrough the screen 112, depositing the particulates and returning to thesurface via the crossover tool 202 through a tubing-casing annulus 206.Upon completion of placing the gravel pack 114, the crossover tool 202is closed, replaced with a production packer, or subjected to otheroperations as known in the art. The placement of the gravel pack 114 asshown in FIG. 2 is exemplary only.

FIG. 3A is a schematic diagram of one embodiment of a device fordepositing particulates 118, 120 between an outer surface of a screen112 and a surface of a formation of interest 106 in a first position.The screen 112 illustrated in FIG. 3A has slots 302 that can beselectively opened or closed or otherwise activated and/or deactivatedfrom the surface in some manner. For example the slots 302 may beengageable through electronic signals, hydraulic signals, actuatedthrough a wireline, actuated through force communicated through thetubing 132 (e.g. downward force, upward force, and/or rotational force),and/or through any other operations understood in the art. In the firstposition as illustrated in FIG. 3A, the slots 302 are open allowingslurry 116 to flow into the screen 112 annulus 203 and thereby depositparticulates 118, 120. As shown in FIG. 3A, the slurry 116 carrier fluid122 flows into the formation of interest 106, typically at an injectingpressure below the fracturing pressure, until the gravel pack 114 isfully placed.

The arrangement illustrated in FIG. 3A is exemplary only. With certaintools and arrangements the carrier fluid 122 may be returned directly tothe surface instead of being injected into the formation of interest106. For example, the slurry 116 may be pumped down the tubing-casingannulus 206, recirculated through the slots to tubing 132 and returnedto the surface. Alternatively, the slurry 116 may be pumped down thetubing 132, forced out of the slots and recirculated through the screen,crossing over into the tubing-casing annulus 206 and returning to thesurface. Each of these arrangements is well understood in the art and isnot shown in FIG. 3A to avoid obscuring aspects of the presentapplication.

FIG. 3B is a schematic diagram of one embodiment of a device fordepositing particulates 118, 120 between an outer surface of a screen112 and a formation of interest 106 in a second position. In the secondposition as illustrated in FIG. 3B, the slots 302 are closed, preventingthe flow of carrier fluid 122 or slurry 116 through the slots. In theembodiment illustrated in FIG. 3B, formation fluid coming from theformation of interest 106 flows through the gravel pack 114 and screen112, preventing sand or unconsolidated particulates from the formationof interest 106 from flowing into the wellbore or tubing 132. In theembodiment of FIG. 3B, any particles 118, 120 that may have settledinside the screen 112 may be cleaned out by recirculation (e.g. with acoiled tubing unit) and/or by entrainment within produced fluid from theformation of interest 106.

FIG. 4A is a schematic diagram of one embodiment of a device fordepositing particulates 118, 120 between an outer surface of a screen112 and a formation of interest 106 in a first position. In theembodiment of FIG. 4A, a specified amount of slurry 116 is placed in thewellbore. The specified amount of slurry 116 depends upon theparticulate loading of the slurry, the diameter of the wellbore, thelength of the interval to be covered, the displacing volume of thescreen 112 (which is lowered into the slurry 116), and similarparameters understood in the art. In certain embodiments, the slurry 116placed at the bottom of the wellbore has a very high particulateloading, for example in excess of 3.6 kg of particulates 118, 120 perliter of carrier fluid 122. The screen 112 in the first positionincludes the screen 112 in position to be lowered into the slurry 116but not yet placed in the slurry 116.

FIG. 4B is a schematic diagram of one embodiment of a device fordepositing particulates 118, 120 between an outer surface of a screen112 and a formation of interest 106 in a second position. The screen 112in the second position includes the screen 112 lowered into the slurry116. In certain embodiments, the screen 112 may include centralizerssuch that the screen 112 is approximately centered in the wellbore.However, where the slurry 116 is dense from heavy particulate loading,the screen 112 tends to self-centralize and external centralizers maynot be required.

FIG. 4C is a schematic diagram of one embodiment of a device fordepositing particulates 118, 120 between an outer surface of a screen112 and a formation of interest in a third position. In the thirdposition, the screen 112 remains in the slurry 116, and productionequipment (for example a production packer 402) is placed in thewellbore to prepare the system for production. In certain embodiments,the well is shut in for a specified time period to allow particulates118, 120 in the slurry 116 to settle, to allow degradable particulatesto decompose completely or partially, to allow carrier fluid 122breakers to act on the carrier fluid 122, and/or to allow particulateswith tackifiers to cure (e.g. with resin-coated particulates).

In certain embodiments, the slurry placement includes a “bottoms-up”method of pumping, which allows for gravel packing and/or fracturingimmediately post-drilling, for gravel packing-while cementing, for theinclusion of chemical packers, and/or for the use of large diameterscreens. FIG. 5 is an illustration of one embodiment of a device 310comprising a generally cylindrical screen 312 positioned in a wellbore314 forming an annulus 316 between the screen and the wellbore. In thisembodiment, the wellbore 314 has a casing 318 cemented above an openhole and the screen 312 is disposed open hole below the casing 318 atthe lower end of a pipe string 320, which can be a workstring,production tubing or the like. The embodiment is equally applicable tocased holes, which are generally perforated for communication with thesurrounding formation 322, as well as non-horizontal wells. Ahigh-solids slurry 324 comprising at least first and second particlescan be passed through a central flow passage 326 through the screen 312to discharge near what is referred to herein as the distal or bottom end328 of the screen 312, into the annulus 316 to be deposited on an outersurface of the screen. Once deposited in the annulus 316, the packedslurry solids can be converted to a gravel pack as described herein.

In one embodiment, “two-trip” gravel packing is achieved by using aworkstring containing a packer assembly and washpipe to place theslurry/gravel and then removing the workstring and washpipe to attachproduction tubing. FIGS. 6A and 6B illustrate one embodiment of abottoms-up placement apparatus similar to FIG. 5, wherein the pipestring 320 comprises a work string including drill pipe 330, a servicetool 332 including packer 334, the screen 312, washpipe 336 and end cap338, which allows the washpipe 336 to connect to the bottom of theassembly. Once in place as shown in FIG. 6A, slurry 324 is pumped downthe drill pipe 330, through the washpipe 336, out the bottom of theassembly 332, and up into the annulus 316 between the open hole of thewellbore 314 and screen 312. After the proper amount of slurry ispumped, the packer 334 is set (see FIG. 6B), and the drill pipe 330,service tool assembly 332, and washpipe 336 are removed from the hole.The slurry 324 is converted into a gravel pack through methods describedherein, for example, by self-triggered degradation, or through asuitable triggering fluid such as an acid, base, solvent, or otherchemical. The embodiment shown in FIGS. 6A and 6B allows placing agravel pack allows for a narrower gap between the screen 312 outerdiameter and the well bore 314. For example, the gravel pack can have athickness (radial thickness in annulus=wellbore radius−screen radius) assmall as 10, 5 or even 3 times the median size of the gravel or othercoarse fraction. In another embodiment, the thickness is less than 50 mm(2-in.) or less than 25 mm (1-in.). In a further embodiment, the gravelpack thickness is from about 6 to about 40 times the median size of thegravel or other coarse fraction of the slurry solids. In one specificembodiment, the gravel pack thickness is from 6 to 25 mm. The narrow gapmeans a larger screen 312 can be employed, and therefore a largerbasepipe inside diameter, improving production of the well. For examplethe basepipe ID can be from 50 to 90 mm larger than a conventionalgravel pack that is more than 50.8 mm (2-in.) thick.

Furthermore, the gravel pack can be pumped into formations 322 where thepore pressure is low, where other methods of gravel packing may lead toinadvertent formation fracturing. For example, some conventional gravelpacking methods may require a relatively high injection rate, e.g. 1600L/min (10 BPM), to maintain the gravel in suspension and preventpremature settling or bridging. In embodiments of the present inventionwherein the slurry is stable and the solids do not easily settle, therate can be selected for the optimum gravel placement, e.g. any non-zeroinjection rate less than 1600 L/min, 800 L/min, 600 L/min, 500 L/min,400 L/min, 300 L/min, 250 L/min, 200 L/min, 150 L/min, 100 L/min, 50L/min (less than 10, 5, 3.8, 3.1, 2.5, 1.9, 1.6, 1.3, 0.94, 0.63bbl/min) or the like.

FIG. 7 is an illustration of one embodiment of a bottoms-up placementapparatus similar to FIGS. 6A and 6B wherein the packer 334 has been setbefore pumping the slurry 324 and the pressure built up in the region ofannulus 316 while pumping the slurry to induce creation of the fracture340 in the adjacent formation 322. The slurry 324 in an embodiment ispumped into the fracture 340 and subsequently converted to a gravelproppant pack as described herein.

In one embodiment, the slurry placement/gravel packing is achieved as apart of the final production run. This embodiment of the method caneliminate the need for a dedicated gravel pack run. Once the slurry isconverted to a gravel pack in this embodiment, production can usuallybegin immediately. The slurry is placed using a bottoms-up placementapparatus similar to FIG. 5, wherein the screens are run in hole using aproduction assembly including production tubing complete withappropriate production accessories, and wherein the screen 312 isblocked with a device or material 342 such that inflow is eliminated andthe screen assembly is essentially a tubular flow conduit. In anembodiment shown in FIG. 8A, the screen 312 is an assembly of aperforated base pipe 344, axial profile rods 346, screen element 348,and outer coating 342. The coating 342 can be, for example, a thinimpermeable sheet of film of a degradable material such as polylactide(PLA), polyglycolide (PGA), or another material that can plug the screenopenings temporarily for gravel placement, but which can then bedegraded or dissolved for production. As another example, the degradablematerial can alternatively and/or additionally be placed as plugs orbridges in the respective openings of the screens and/or between thescreen element 348 and the base pipe 344, e.g., by dipping or sprayingor otherwise applying a removable solid- or film-forming material to theassembled screen 312 (see the discussion of FIGS. 20 to 22 below forplugging or bridging the screen openings down-hole), or prior to finalassembly, the screen element 348 and/or base pipe 344.

Once the assembly is in place, slurry is pumped down the tubing; throughthe flow passage in the screen 312, which can be located centrallywithin the screen element or peripherally adjacent the screen element;out the bottom of the assembly, which can comprise an opening throughthe end 328; and up into the area of the annulus 316 between the openhole 320 and screen 312, as shown schematically in FIG. 5. After theproper amount of slurry 324 is pumped, the packer is set, the slurry isconverted to a gravel pack, and also the coating 342 is removed to openthe screen 312, as seen in FIG. 8B. The slurry is converted into agravel pack through methods described herein, either by self-triggereddegradation, or through a suitable triggering signal or fluid such as anacid, base, solvent, or other chemical. Furthermore, any blockage of thescreens 312, e.g. an impermeable surface film or blockage in the throughports, for example—is removed.

FIG. 9 is an illustration of one embodiment of a screen assembly for abottoms-up placement apparatus using a blocked screen similar to FIGS.8A and 8B, wherein the screen 312 contains a degradable or dissolvableplug 350 within the perforations 352 of the base pipe 344 to preventflow across the screen 312 during slurry placement.

FIG. 10 shows fluid flow through the screen elements 348, between theaxial profile rods 346 and through the perforations 352 followingremoval, e.g., by degradation, of the plugs 350.

FIG. 11 is an illustration of another embodiment of a screen assemblyfor a bottoms-up placement apparatus using a blocked screen similar toFIGS. 8A-10, wherein the screen 312 is operatively associated with amechanical inflow-control device (ICD) 354 to control flow through theopenings in the screen 312. The ICD 354 is used with an impermeablebasepipe 344A and can be activated by controller 356 via a suitableremote method such as a slickline or wireline, or the controller 356 canbe a timer to allow flow at a prescribed time after the assembly is runin hole.

FIG. 12 shows fluid flow through the screen elements 348 and the ICD 354following flow actuation. In one embodiment, the slurry placement/gravelpacking is achieved using chemical packers with the gravel pack. As bestseen in the embodiment shown in the schematic diagram of FIG. 13, thescreen 312 is run in hole using apparatus similar to that shown in FIGS.5-12, except that a mechanical packer 334 is not necessarily required.Instead, a chemical compound slug 360 is run ahead of a slurry volume362, such that at the appropriate time the chemical slug 360 sealsbetween the tubing 320 and the annulus 316, concentrating productionflow through the screen 312. The chemical compound slug 360 can includein some embodiments, phenolic resins, urethane compounds or the like,that are known to the art for employment in chemical packers and bridgeplugs. In one embodiment, the workstring 320 comprises productiontubing. If desired, in an embodiment, additional spacer chemicalcompound slugs 364 can be alternated with slurry volumes 362 to obtainintermittent spacing of resin plugs within the gravel pack and thuscreate zonal isolation.

FIG. 14 is an illustration of another embodiment of a screen assemblyfor a bottoms-up placement apparatus using a chemical resin plugs 360and/or 364 similar to FIG. 13, except that the assembly includes one ormore diversion ports 366 above the screen 312, which can be activated bytraditional mechanical means, e.g., a ball, sleeve, wireline, or thelike. The chemical resin plug 360 is not necessarily pumped ahead of theslurry volume 362, but can alternatively or additionally be pumpedthrough the diversion port 366. This facilitates precise placement ofthe slug 360 in a prescribed position above the screen 312.

In one embodiment, the slurry placement/gravel packing is achieved as apart of the drilling process. This embodiment of the method caneliminate the need for a dedicated gravel pack run, and in a furtherembodiment the screen 312 is placed in the same manner as a slottedliner would be. FIG. 15 is an illustration of one embodiment of abottoms-up placement apparatus similar to FIG. 5, wherein the screensare run in hole using a drilling assembly wherein the workstring 320comprises drill pipe complete with appropriate drilling accessories,such as, for example, a liner packer 334 as discussed in connection withFIGS. 6A to 7, screen 312, and a drill bit assembly 368, which can alsoinclude measurement-while-drilling capability. The screens 312 inalternate embodiments may or may not have restricted inflow as discussedin connection with FIGS. 8A to 12, e.g., a film outside the screens,plugs within the base pipe, or mechanical and/or timed inflow controldevices.

The final length of the hole 314 is drilled with the screens 312 asshown in FIG. 15, and once on depth, the drill bit 368 is abandoned downhole. The slurry is then pumped through the drill bit 368, and up theannulus 316. If desired, any plugging material can follow the slurry toseal off the bottom of the hole 314 below the drill bit 368. The linerpacker 334 is then set, the slurry is converted to a gravel pack asdescribed herein, production tubing is put in place and productioninitiated. In an alternative embodiment, the liner packer 334 can be setfirst to initiate hydraulic fracturing as discussed in connection withFIG. 7 above, and the slurry is transformed into a gravel/proppant pack.As further alternatives, chemical packers and spacers can additionallyor alternatively to the liner packer 334 be employed as discussed inconnection with FIGS. 13 and 14. In addition to eliminating the need fora dedicated gravel pack run, as well as placing the screens in the samemanner as a slotted liner would be, the large ID of the screens canallow a greater inflow and therefore a greater production through thetubing.

FIG. 16 is an illustration of one embodiment of a carrier fluid 122combined with a first 118, second 120, and third 502 amount of particlesin a slurry 116. The particulates 118, 120, 502 in an embodimentcomprise three size regimes, wherein each size regime is three tofifteen times larger than the next smaller size regime. The inclusion ofvarying size particulates 118, 120, 502, with a high particulateloading, creates a slurry 116 with greatly reduced settling timesrelative to a slurry 116 with a uniform particle size.

Further, the amount of carrier fluid 122 per unit volume of slurry 116can be reduced dramatically. For example, spherical particles with auniform packing arrangement create a packing volume fraction (PVF) ofabout 0.74, i.e., where about 74% of the slurry volume is particulatematter. Monodisperse spherical particles with a random close packingarrangement create a PVF of about 0.64. By contrast, an arrangement withthree particulate sizes having average diameters, in one example, of 840microns, 150 microns, and 15 microns, respectively, creates a mixture ofparticles having a PVF of about 0.87. The base densities of theparticles 118, 120, 502 may be selected to create a final slurry densityat a selected value. An increase in PVF reduces the amount of carrierfluid 122 in the final slurry 116. For example, an increase from 0.64(random packing) to just 0.80 reduces the amount of carrier fluid 122 ina liter of slurry by nearly 50% (i.e. (36−20)/36). The reduced carrierfluid 122 amount reduces the amount of fluid placed in the formation ofinterest 106 and the amount of viscosifier (if any) in the gravel pack114, which all contribute to a reduction in permeability damage to theformation of interest 106 and a reduction in permeability damage to thegravel pack 114.

In certain embodiments, the slurry 116 includes at least a first amountof particulates 118 having a first average size distribution and asecond amount of particulates 120 having a second average sizedistribution. In certain embodiments, the first amount of particulates118 are non-deformable particulates. The average size distribution isdetermined according to any method understood in the art, at leastincluding a mesh screen size number (e.g., 16/30 mesh sand, 20/40 meshsand or 40/70 mesh sand), a mean particle size, and a median particlesize. The average size distributions of the first amount of particulates118 and the second amount of particulates 120 are selected in anembodiment such that the first average size distribution is betweenthree and fifteen times larger than the second average sizedistribution. The average size distributions of the first amount ofparticulates 118 and the second amount of particulates 120 are furtherselected to prevent migration of formation fines through the gravel pack114 into the well 102. In certain embodiments, a larger sizedistribution (e.g. the first size distribution to the second sizedistribution, or the second size distribution to a third sizedistribution) is a value between six and ten times larger. Distributionsbetween six and ten times in this embodiment allow maximal packed volumefraction (PVF) values while providing a gravel pack that does notshrink, or lose pack efficiency, if smaller particle sizes are removed.

In certain embodiments, the slurry 116 includes a third amount ofparticulates having a third average size distribution, where the secondaverage size distribution is larger than the third size distribution,for example, between three and fifteen times larger than the third sizedistribution. For example, the first average size distribution may be amedian size of about 840 microns, the second average size distributionmay be a median size of about 150 microns, and the third average sizedistribution may be a median size of about 15 microns.

In certain embodiments, the slurry 116 includes a fourth and/or a fifthamount of particulates. The fourth amount of particulates in oneembodiment includes a fourth average size distribution that is smallerthan the third average size distribution, for example, between three andfifteen times smaller than the third average size distribution. Thefifth amount of particulates in one embodiment includes a fifth averagesize distribution that is smaller than the fourth average sizedistribution, for example, between three and fifteen times smaller thanthe fourth average size distribution.

In a further embodiment, the solids mixture comprises four or more PSDmodes to form the bridge on the screen, wherein a first amount ofparticulates have a first PSD, a second amount of particulates have asecond PSD, a third amount of particulates have a third PSD, and afourth amount of particulates have a fourth PSD, wherein the firstaverage size distribution is at least three times larger than the secondaverage size distribution, wherein the second average size distributionis larger than the third average size distribution, preferably at leastthree times larger than the third average size distribution, and whereinthe third average size distribution is larger than the fourth averagesize distribution, preferably from three to fifteen times larger thanthe fourth average size distribution. In one embodiment, the firstaverage size distribution is 40 mesh (422 micron) or larger, and inanother comprises standard 20/40 mesh (422-853 microns) gravel. In oneexample, the first PSD is about 280 microns, the second PSD about 30microns and the third PSD about 3 microns. In one embodiment, a ratio ofthe total solids volume of the first particles to the total solidsvolume of the second particles is from about 1:1 to about 15:1,preferably from about 2:1 to about 10:1 or from about 4:1 to about 8:1;and a ratio of the total solids volume of the second particles to thetotal solids volume of the third particles is from about 1:10 to about2:1, preferably from about 1:4 to about 1:1.

In another embodiment, a carrier fluid and a solids mixture are combinedto form a flowable slurry adapted to form a bridge on a screen toinhibit fluid entry while the screen and the slurry are disposed in awellbore, in any order. In an embodiment the solids mixture comprises aplurality of volume-averaged particle size distribution (PSD) modes suchthat a packed volume fraction (PVF) of the solids mixture exceeds 0.75,or preferably exceeds 0.8. In an embodiment, the solids mixturecomprises three or more PSD modes to form the bridge on the screen,wherein a first amount of particulates have a first PSD, a second amountof particulates have a second PSD, and a third amount of particulateshave a third PSD, wherein the first PSD is from two to ten times largerthan the second PSD, and wherein second PSD is from three to ten timeslarger than the third PSD. In one embodiment, the first amount ofparticulates is smaller than about 40 mesh (422 microns), and in anotherembodiment the first amount of particulates comprises 40/80 mesh(178-422 microns) gravel. In one example, the first PSD is about 280microns, the second PSD about 30 microns and the third PSD about 3microns. In one embodiment, a ratio of the total solids volume of thefirst particles to the total solids volume of the second particles isfrom about 1:1 to about 15:1, preferably from about 2:1 to about 10:1 orfrom about 4:1 to about 8:1; and a ratio of the total solids volume ofthe second particles to the total solids volume of the third particlesis from about 1:10 to about 2:1, preferably from about 1:4 to about 1:1.

The median size used herein may be any value understood in the art,including for example and without limitation a diameter of roughlyspherical particulates. In certain embodiments, the median size may be acharacteristic dimension, which may be a dimension considered mostdescriptive of the particles for specifying a size distribution range.In certain embodiments, the first amount of particulates have acharacteristic dimension, for example and without limitation a medianparticle diameter, between about 500 microns and 1800 microns. Incertain embodiments, the first amount of particulates includes a medianparticle volume between about 2×10⁻¹¹ m³ and 6×10⁻¹⁰ m³. Other volumeranges will be understood by those of skill in the art to be functionalaccording to the principles described herein, and all relevant values ofparticles sizes for gravel packing are contemplated herein.

In certain embodiments, each median size is a characteristic dimension,where the ratio of characteristic dimensions between particle sizes(e.g. first amount of particulates compared to second amount ofparticulates) is proportional to a cube root of a ratio of averageparticle volumes between particle sizes. For example, the first amountof particulates may have a characteristic dimension of 1.5×10⁻³ m and anaverage particle volume of 5.63×10⁻¹⁰ m³. The second amount ofparticulates in the example has an average particle volume between about1.7×10⁻¹³ m³ to 2.1×10⁻¹¹ m³, with a characteristic dimension between1×10⁻⁴ m and 5×10⁻⁴ m which includes the range from one-third toone-fifteenth the characteristic dimension of the first amount ofparticulates.

The characteristic dimension is used herein to more clearly indicatethat the size selection of the particles in the first and second (and/orthird, fourth, and fifth) particulate amounts are independent of theshape of the particles. Therefore, in various embodiments the particlesizes can vary in each particle size step by three to fifteen times inany average linear measure, and/or by 3³ times to 15³ times (i.e. 27 to3375 times). The relative sizing of the particulates in embodiments maymeet either the linear criteria 3 to 15 times, or the volumetriccriteria 3³ times to 15³ times, or both. In certain embodiments,utilizing a narrower range of 5 to 10 times (characteristic dimension orlinear measure) provides greater settling time improvement and thereforeallows higher particulate loadings and/or lower carrier fluid 122viscosities.

The carrier fluid 122 may in various embodiments be a brine, a fluidincluding a hydratable gel (e.g. a guar, other polysaccharide,hydroxyethyl-cellulose “HEC”, or other gelling agent), an oil oroil-based gel, a viscoelastic surfactant, a fluid with a viscosifier, afoamed or “energized” fluid (e.g. a nitrogen or CO₂ based foam), anemulsion (including water or oil in the external phase), or other fluidknown in the art.

In certain embodiments, the mixing of particulates 118, 120 with sizeratios as described herein allows high particulate loadings with a lowor zero viscosifier loading. In certain embodiments, the carrier fluid122 includes a brine with no viscosifiers, and the sum of the mass ofthe particulates (i.e. the first amount, second amount, and/or any thirdor other amounts combined) is at least about 2.4 kg per liter of carrierfluid 122 (20 pounds per gallon). In certain embodiments, the carrierfluid includes a hydratable gelling agent present in an amount less thanabout 2.4 g gel per liter of carrier fluid (20 lb gel per 1000 gallons),for example less than 2.15 g/L (18 lb gel per 1000 gallons of carrierfluid), and the sum of the mass of the particulates exceeds about 2.75kg per liter (23 pounds per gallon) of carrier fluid 122. In certainembodiments, the carrier fluid 122 includes a viscosifier present in anamount less than 20 lb per thousand gallons of carrier fluid 122, andthe sum of the mass of the particulates exceeds about 2.75 kg per liter(23 pounds per gallon) of carrier fluid 122. In certain embodiments, thecarrier fluid 122 includes a viscosifier present in an amount less than2.4 g gel per liter (20 lb gel per 1000 gallons) of carrier fluid 122,and the sum of the mass of the particulates exceeds about 3.6 kg perliter (30 pounds per gallon) of carrier fluid 122.

In an embodiment, the solids loading in the slurry can be expressed as avolumetric ratio of solids to carrier fluid. In one embodiment, aminimum volume of the liquid (maximum volumetric solids loading)corresponds to the solids:carrier fluid volumetric ratio in the slurrycorresponding to the PVF for the solids mixture, i.e. PVF:(1−PVF), or aslight excess of liquid to impart rheological characteristics to theslurry, whereas too much excess carrier liquid might induce instabilityof the slurry (solids settling or syneresis). In one embodiment, thesolids:carrier fluid volumetric ratio is from about 40:60 up toPVF:(1−PVF), and in another embodiment from 45:55 to 85:15. In otherembodiments, the volume fraction of the carrier fluid is fromstoichiometric (1−PVF) or from above stoichiometric up to 3, 2.5, 2,1.5, 1.25, 1.2, 1.1 or 1.05 times stoichiometric, or stated differently,the volumetric solids fraction is from (3PVF−2), (2.5PVF−1.5), (2PVF−1),(1.5PVF−0.5), (1.25PVF−0.25), (1.2PVF−0.2), (1.1PVF−0.1) or(1.05PVF−0.05) up to PVF.

The limits for minimum viscosifier loading and maximum particulateloading depend upon factors specific to each system 100 that willordinarily be understood or controlled by those of skill in the art. Forexample, the settling time of the particulates 118, 120 in the carrierfluid 122, the viscosity of the carrier fluid 122, the intended pumpingrate of the slurry 116, the length of the screen 112 interval whereinthe gravel pack 114 is to be placed, the fracture strength of theformation of interest 106, and other factors known to those of skill inthe art all contribute to the viscosifier loading required in aparticular application. Using only brine as a carrier fluid 122 with thelayered particulate sizes 118,120, including a third and/or additionalparticulate sizes, slurries 116 have been developed with particulatesexceeding 2.4 kg per liter (20 lb per gallon) of carrier fluid 122, andin certain applications the particulates can exceed 3.6 kg per liter (30lb per gallon) of carrier fluid 122. In certain embodiments, at leastone of the smaller particulate sizes (i.e. the second, third, fourth,and/or fifth amount of particulates) include a degradable material. Theinclusion of degradable material allows the particulates to participatein improving suspension of particles in the slurry 116, while allowingthe particles to be removed in the gravel pack 114 after placement,and/or to allow the particles to release beneficial chemicals into thegravel pack 114 after placement. For example, the degradation of theparticulates may release chemicals that dissolve bridging agents, breakcrosslinked or polymer-based carrier fluid 122, and/or that attack afilter cake formed.

Examples of degradable materials include, without limitation, wax,oil-soluble resin, materials soluble in hydrocarbons, lactide,glycolide, aliphatic polyester, poly(lactide), poly(glycolide),poly(ε-caprolactone), poly(orthoester), poly(hydroxybutyrate), aliphaticpolycarbonate, poly(phosphazene), poly(anhydride), poly(saccharide),dextran, cellulose, chitin, chitosan, protein, poly(amino acid),polyethylene oxide), and copolymers including polylactic acids) and/orpoly(glycolic acids), and the like. In certain embodiments, degradablematerials may include a copolymer including a first moiety that is ahydroxyl group, a carboxylic acid group, and/or a hydrocarboxylic acidgroup, and a second moiety that is a glycolic acid and/or a lactic acid.

In certain further embodiments, at least one of the smaller particulatesizes includes a reactive solid that reacts with a hydrolysis product ofa degradable material. For example, the second amount of particulates120 may be a degradable material and the third amount of particulatesmay be a material that reacts with the hydrolysis product of the secondamount of particulates 120, enhancing the rate of degradation of thesecond amount of particulates 120. In certain embodiments, the reactivesolid includes ground quartz, oil soluble resin, degradable rock salt,clay, and/or zeolite or the like. In certain embodiments, the reactivesolid includes magnesium hydroxide, magnesium carbonate, magnesiumcalcium carbonate, calcium carbonate, aluminum hydroxide, calciumoxalate, calcium phosphate, aluminum metaphosphate, sodium zincpotassium polyphosphate glass, and/or sodium calcium magnesiumpolyphosphate glass or the like. The degradable materials and reactivesolids that enhance degradation may be stored on the same particle, suchthat reactions do not occur at the surface but begin within the fluidsat downhole conditions.

In certain embodiments, the slurry comprises a carrier fluid and asolids mixture, wherein the solids mixture comprises a plurality ofvolume-averaged particle size distribution (PSD) modes, wherein a firstPSD mode comprises solids having a volume-average median size at leastthree times larger than the volume-average median size of a second PSDmode such that a packed volume fraction (PVF) of the solids mixtureexceeds 0.75 or preferably exceeds 0.8, and wherein the solids mixture,preferably the second PSD mode, comprises a degradable material andincludes a reactive solid.

In one embodiment, the first PSD mode comprises gravel and the secondPSD mode comprises alumina trihydrate particles. Alumina trihydrateparticles become soluble at elevated or depressed pH, and thus can bedegraded by changing a pH in the pack to solubilize the aluminatrihydrate particles. In another embodiment, the degradable material canbe soluble in either basic or acidic fluids, and can be degraded byincreasing or decreasing the pH, respectively, to dissolve theparticles, e.g., by contacting the solids pack with a basic aqueoussolution or an acidic aqueous solution. For example, the degradablematerial can be selected from amphoteric oxides, esters, coated acids,combinations thereof, and the like. Acid precursors which can bementioned as suitable particulates include hydrolyzable esters, acidanhydrides, acid sulfonates, acid halides, combinations thereof and thelike. As another example, the solids mixture can include a base or baseprecursor, which can in some embodiments be sparingly soluble orencapsulated. Representative classes of bases include alkali metal andammonium hydroxides, organic amines, urea, substituted urea,combinations thereof and the like. Specific representative examples ofacid soluble particulates include oxides and hydroxides of aluminum,zinc, tin, lead, boron, silicon and iron; carbonates, sulfates, oxidesand hydroxides of calcium, magnesium and barium; combinations thereofand the like.

In one embodiment, the degradable second PSD mode can be or include anencapsulated water- or oil-soluble solid, and can be degraded byde-encapsulating the soluble solid and contacting the solids pack withaqueous or hydrocarbon fluid, e.g., with reservoir fluids. In anotherembodiment, the degradable particulates can be or include awater-soluble solid and the carrier fluid can be a saturated aqueoussolution of the water-soluble solid, whereby degradation can be effectedby contacting the pack with an undersaturated aqueous medium. Forexample, the soluble particulates can be or include salt and the carrierfluid can be brine. In another embodiment, the degradable particulatescan be or include a water-soluble solid, and the carrier fluid can be aninvert oil emulsion wherein the water-soluble solid is dispersed in anoil phase, whereby the degradation can be effected by breaking theemulsion to dissolve the water-soluble solid in an aqueous medium. Theemulsion can be broken, for example, by contacting the pack with ade-emulsifier, pH control agent or the like. Representative pH controlagents which may be mentioned include monoesters, polyesters, weakacids, weak bases, urea, urea derivatives, combinations thereof and thelike.

In certain embodiments, at least one of the amount of particulates(e.g., first through fifth) includes an encapsulated breaker thatreduces the viscosity of the carrier fluid 122 after placement of thegravel pack 114 reducing permeability damage of the pack 114. In certainembodiments, the carrier fluid 122 includes an emulsion, and at leastone of the amount of particulates includes a chemical adapted to assistin breaking the emulsion. In certain further embodiments, the chemicaladapted to assist in breaking the emulsion is encapsulated and/orincluded on a coated particle, such that the chemical is not released tobreak the emulsion until after the gravel pack 114 is placed. In certainfurther embodiments, one or more of the amount of particulates comprisescoated particles, such that the particles do not begin to degrade and/orrelease chemicals, breakers, solvents, and/or surfactants or the likeuntil after the gravel pack 114 is placed. Any coating on a particle maybe adapted to break down with time, temperature, fluids expected to beencountered in the wellbore, chemicals or reactive solids included onother particles and/or in the carrier fluid 122 that are released underother mechanisms.

In one exemplary embodiment, the carrier fluid 122 comprises anemulsion, the second amount of particulates includes a surfactant thatbreaks the emulsion and the second amount of particulates are coatedwith a material that breaks down in the presence of a chemical in thethird amount of particulates. In the example, the third amount ofparticulates includes a coating that degrades in the presence ofhydrocarbons (e.g. as produced from the formation of interest 106) thatreleases the chemical breaking down the coating on the second amount ofparticulates. Similar configurations of particles, coatings, chemicals,and the like are contemplated in the present application.

In certain embodiments, one or more of the particulates includes aformation face damage removal agent. The damage removal agent may be achemical (e.g. an acid and/or an oxidizer) structured to removeformation face damage, and/or a physical agent (e.g. particles of aspecific shape, size, or material to break an emulsion). The damageremoval agent may be any damage removal material known in the art, andmay be included in any of the particulates. Further, and withoutlimitation, the damage removal agent may be within a particle thatenters the fluid in the wellbore on dissolution, and/or is embeddedwithin a coated particle. The formation face may have permeabilitydamage from the gravel pack fluid filter cake, from a fluid loss agentin the gravel pack, from a drilling mud filter cake, from a fluid lossagent in the drilling mud, and/or residual damage from a pill (e.g. ahigh viscosity pill pumped during drilling to stop fluid loss) pumpedduring drilling or completion of the wellbore. The fluid loss agent canbe, for example, a latex dispersion of polyvinylidene chloride,polyvinyl acetate, polystyrene-co-butadiene; a water soluble polymersuch as hydroxyethylcellulose (HEC), guar, copolymers of polyacrylamideand their derivatives; particulate fluid loss control agents in the sizerange of 30 nm-1 μm such as γ-alumina, colloidal silica, CaCO₃, SiO₂,bentonite etc.; particulates with different shapes such as glass fibers,flakes, films; and any combination thereof or the like.

In certain embodiments, the amount of particulates 118, 120 compriseparticles having an aspect ratio of greater than or equal to one,preferably greater than or equal to 6, 10, 25, 50, 100, 200 or 300. Incertain embodiments, particles with a higher aspect ratio have enhancedsurface area per unit volume and enhance degradation and/or reactionrates for the particles. In certain embodiments, the amount ofparticulates 118, 120 comprises particles having a nano-structure,micro-structure, or mesoporous structure that enhance the surface areaof the particles. The structures of the particles may be fractal ornon-fractal. In certain embodiments, at least one of the particulates118, 120 includes a tackifying agent such as a resin-coating.

FIG. 17 is an illustration of one embodiment of a carrier fluid 122combined with a first 118, second 120, and third 502 amount of particlesin a slurry. In the illustration of FIG. 17, the second amount ofparticulates 120 include particulates having an aspect ratio greaterthan one. The aspect ratio may be defined in any direction desired. Inthe second amount of particles 120 illustrated in FIG. 17, the particlesare elongated, but may comprise flakes, disks, ellipsoids, fibers, orany other particulate shapes known in the art. Any of the first amountof particulates 118, second amount of particulates 120, third amount ofparticulates 502, the fourth amount of particulates (not shown), and/orthe fifth amount of particulates (not shown) may comprise anon-spherical shape. In certain embodiments, the first amount ofparticulates 118 comprise the primary particulate making up the“gravel,” and the first amount of particulates 118 are approximatelyspherical to maximize permeability of the gravel pack 114.

The schematic flow diagram and related description which followsprovides an illustrative embodiment of performing operations for lowdamage gravel packing. Operations illustrated are understood to beexemplary only, and operations may be combined or divided, and added orremoved, as well as re-ordered in whole or part, unless statedexplicitly to the contrary herein.

FIG. 18 is a schematic flow diagram of one embodiment of a procedure 700for low damage gravel packing. The procedure 700 includes an operation702 to combine a carrier fluid, a first amount of particulates, and asecond amount of particulates into a slurry, where the first amount ofparticulates have a first average size distribution and the secondamount of particulates have a second average size distribution, wherethe first average size distribution is at least five times larger thanthe second average size distribution, and where the first amount ofparticulates comprise non-deformable particulates. In certain furtherembodiments, the procedure 700 includes an operation 704 to combine athird amount of particulates with the slurry, where the third amount ofparticulates have a third average size distribution, and where thesecond average size distribution is at least five times larger than thethird average size distribution.

The method 700 further includes an operation 706 to position a screen ina wellbore, and an operation 708 to circulate slurry through thewellbore such that the first amount of particulates and the secondamount of particulates are deposited on an outer surface of the screen.In different embodiments, operations 706 and 708 can be implanted ineither order, e.g., by first circulating the slurry into the wellboreand then positioning the screen in the slurry. In certain embodiments,circulating the slurry through the wellbore comprises flowing the slurryinto a formation of interest, and flowing the slurry back out of theformation of interest such that particulates from the slurry aredeposited on the outer surface of the screen.

FIGS. 19A and 19B are schematic flow diagrams of two related embodimentsof techniques 800A, 800B for low damage gravel packing. The techniques800A, 800B include an operation 802 to combine a carrier fluid, a firstamount of particulates, a second amount of particulates, and/or a thirdamount of particulates into a slurry. The first amount of particulateshave a first average size distribution, the second amount ofparticulates have a second average size distribution, and the thirdamount of particulates have a third average size distribution. In anembodiment, the first average size distribution is at least three timeslarger than the second average size distribution, and the first amountof particulates comprise non-deformable particulates. The second averagesize distribution is larger than the third average size distribution,preferably at least three times larger. The technique 800A (FIG. 19A) inone embodiment further includes an operation 804 to position a screen ina wellbore, followed by an operation 806 to deposit each of the amountsof particulates between an outer surface of the screen and a surface ofthe wellbore. The technique 800B (FIG. 19B) in one embodimentalternatively includes an operation 808 to position an amount of slurryin the wellbore, followed by an operation 810 to position the screen inthe amount of slurry. In certain embodiments, the techniques 800A, 800Binclude operation 812 to set a production packer, and operation 814 todisplace a slurry remainder inside the screen and/or operation 816 toshut in the wellbore for a specific period, e.g., to degrade or dissolveparticulates in some embodiments. In certain embodiments, the simplifiedoperations (relative to currently available gravel packing operations)of placing the slurry 116 in the wellbore and the screen 112 into theslurry allow a very low carrier fluid 122 viscosifier loading andrequire a high particulate loading (as in certain embodiments excesscarrier fluid 122 is not pumped into the formation of interest 106). Incertain embodiments, the carrier fluid 122 includes viscosifiers at lessthan 2.4 g/L (20 lb/1000 gals), and total particulate loadings above 3.6kg/L (30 ppg). In certain embodiments, the slurry 116 includesparticulate amounts (for the first, second, third, fourth, and/or fifthamount of particulates) and sizes such that the packed volume fraction(PVF) for the slurry 116 is greater than 0.75 PVF, or in someembodiments greater than 0.8 PVF.

Displacing the slurry remainder inside the screen includes circulatingout particulates inside the screen 112, and/or flowing formation fluidfrom the formation of interest 106 and thereby carrying any slurryremainder out of the screen 112. In certain embodiments, at least one ofthe second and third particulate amounts comprise a degradable material,and the technique 800 further includes an operation 816 to shut in thewellbore for a specified time period. In certain embodiments, thespecified time period may be a time period selected such that variousdegradation and breaking reactions have time to occur before flowingfluids out of the wellbore.

According to one embodiment, as mentioned above, the screen is treatedwith a leak-off control agent to limit fluid loss into the screen fromthe multimodal slurry during placement thereof, which might otherwiseresult in premature bridging of the slurry due to fluid loss. Withreference to FIG. 20, the multimodal slurry 324 is introduced into thebottom of the bore hole 314, and a spacer fluid 380 is placed in thewell above the slurry 324. The spacer fluid 380 contains one or moreleak-off control agents, small particles or a range of particle sizessuitable for plugging or bridging the openings in the screen elements ofthe screen assembly 312. As the screen 312 is lowered in the well bore314, it initially passes through the spacer fluid 380 and the leak-offcontrol agent seals off the openings in the screen 312 to limit furtherfluid entry so that when the screen 312 enters the slurry 324 the slurryremains fluid and the screen 312 mobile therein until the screen can beplaced in the well bore 314 as desired. After the screen 312 is properlypositioned in the well bore 314, the leak-off control agent is degradedby dissolution or reaction, for example, or otherwise removed from thescreen to restore permeability for production fluids, and the slurry 324is converted to a permeable gravel pack as described herein forproduction.

The spacer fluid 380, in addition to the leak-off control agent,stability agent, dispersant or the like, can contain various componentsand additives well known to be present in treatment fluids, includingwater, brine, oil, emulsion, invert emulsion, solvents, foaming orenergizing agent, viscosifiers, surfactants, crosslinkers, frictionreducers, breakers, accelerators, retarders, antioxidants, pHstabilizers and control agents, etc. In one embodiment, the spacer fluid380 is compatible with the slurry and other fluids used in the wellbore.

In another embodiment, the high-solids slurry is designed such that itlimits leak-off into the screen by forming a bridge on the screen tocontrol dehydration of the slurry. As examples of fluid loss agentswhich can be used to inhibit leak-off from the slurry, either in thespacer fluid or in the slurry itself, there may be mentioned latexdispersions, water soluble polymers, submicron particulates,particulates with an aspect ratio higher than 1, preferably higher than6, combinations thereof and the like, such as, for example, crosslinkedpolyvinyl alcohol microgel. The fluid loss agent can be, for example, alatex dispersion of polyvinylidene chloride, polyvinyl acetate,polystyrene-co-butadiene; a water soluble polymer such ashydroxyethylcellulose (HEC), guar, copolymers of polyacrylamide andtheir derivatives; particulate fluid loss control agents in the sizerange of 30 nm-1 μm such as γ-alumina, colloidal silica, CaCO₃, SiO₂,bentonite etc.; particulates with different shapes such as glass fibers,flakes, films; and any combination thereof or the like. Fluid lossagents can if desired also include or be used in combination withacrylamido-methyl-propane sulfonate polymer (AMPS). In one embodiment,the leak-off control agent comprises a reactive solid, e.g., ahydrolysable material such as PGA, PLA or the like; or it can include asoluble or solubilizable material such as a wax, an oil-soluble resin,or another material soluble in hydrocarbons, or calcium carbonate oranother material soluble at low pH; and so on. In an embodiment, theleak-off control agent comprises a reactive solid selected from groundquartz, oil soluble resin, degradable rock salt, clay, zeolite or thelike. In another embodiment, the leak-off control agent comprisesmagnesium hydroxide, magnesium carbonate, magnesium calcium carbonate,calcium carbonate, aluminum hydroxide, calcium oxalate, calciumphosphate, aluminum metaphosphate, sodium zinc potassium polyphosphateglass, and sodium calcium magnesium polyphosphate glass, or the like. Inone embodiment where the slurry 324 comprises a degradable material, theleak-off control agent comprises the same or a similar material so thatthe leak-off control agent is removed from the surface of the screen 312simultaneously with the degradable material in the slurry, e.g.,concurrently with the second amount and/or third amount of particulateswhere these are present in the slurry.

In another embodiment, with reference to FIGS. 21 and 22, a screen 312is positioned in a wellbore 314 as described above in connection withFIGS. 5 to 7. The spacer fluid 380, which contains a leak-off controlagent as described above, is pumped ahead of the multimodal slurry 324,and introduced into the annulus 316 around the screen 312, e.g., viawash pipe 336 or other suitable means, whereby the openings in thescreen 312 are sealed to limit leak-off. The high-solids slurry 324 isthen introduced into the annulus 316 displacing the spacer fluid 380with controlled leak-off into the screen 312 so that the slurry retainsits rheological characteristics and avoids premature bridging orplugging in the annulus 316, at least until the slurry 324 is placed asdesired. Thereafter, the leak-off control agent is removed from thescreen 312 and the slurry 324 is converted to a gravel pack aspreviously described.

In embodiments, the slurry is comprised of a carrier fluid, a solidsmixture and a stability additive, wherein the solids mixture comprises aplurality of PSD modes such that a packed volume fraction (PVF) exceeds0.75, and preferably exceeds 0.8. The stability additive helps inhibitsettling of the solids mixture in the slurry, and thus maintain itsrheological characteristics. This can be important where the slurry hasto be prepared in advance of use or where the slurry is placed in thewellbore with considerable delay before it contacts the screen, e.g.,where the workstring is tripped out to attach the screen after slurryplacement. The stability additive in one embodiment comprises colloidalparticles, such as, for example, γ-alumina, MgO, γ-Fe2O3, combinationsthereof and the like. In another embodiment, the stability additivecomprises hydratable polymer particles, especially polymer particleswhich are hydrated at downhole temperatures such as above 60° C., forexample, heteropolysaccharides such as gellan gum. Stabilizing particlescan also include particles having an aspect ratio above 6, 10, 20, 50,100, 200, 300 or the like, especially flakes or fibers comprising apolymer or copolymer of lactic acid, glycolic acid, a combinationthereof or the like. In a particular embodiment, the slurry has a solidsvolume fraction (SVF) from 0.5 to 0.75, preferably from 0.55 to 0.7,preferably from 0.56 to 0.68, preferably from 0.58 to 0.66. In variousembodiments, the solids mixture is trimodal, tetramodal, pentamodal orthe like, and can remain stable and flowable for at least 48 hours.

In another embodiment, a dispersant can be used to remove fines from asolids pack formed from a slurry comprising a carrier fluid and a solidsmixture, wherein the solids mixture comprises a plurality ofvolume-averaged particle size distribution (PSD) modes such that apacked volume fraction (PVF) exceeds 0.75, preferably exceeds 0.8, andwherein the solids mixture comprises at least a proppant PSD mode and afines PSD mode. The dispersant can be present in the slurry, in anotherfluid used to displace the carrier fluid from the proppant pack, or in afluid circulated and/or spotted in the wellbore after forming the pack.In an embodiment, the dispersant comprises a polyelectrolyte, forexample, polysulfonate, such as lignosulfonate, polymelamine sulfonate,polystyrene sulfonate, polynaphthalene sulfonate or the like;polycarboxylate, such as a polyacrylate having a weight averagemolecular weight less than 10,000 Daltons; combinations thereof and thelike. In one embodiment, the dispersant comprises a surfactant, e.g., ananionic, cationic, amphoteric, zwitterionic or nonionic surfactant. Atlow concentrations, surfactants can have a coagulating effect on fines,however, at sufficiently high concentrations the surfactants areeffective as fines dispersants. In general, the higher the salinity themore dispersant that is required, especially in regards to the ionicdispersants. Where the carrier fluid is a brine or especially a highbrine, nonionic surfactants such as polyoxyethylenes (includingpolyethylene glycol) may be beneficial since they are less affected bysalinity. In general, a weight ratio between the dispersant and thefines is from about 1:500 to 10:90.

The fines dispersed by the dispersant in various embodiments are silica,calcium carbonate, or the like. The fines can if desired be agglomeratedin the slurry. The slurry can comprise a volume fraction of solids fromabout 0.45 up to the PVF, and a volume fraction of carrier fluid from(1−PVF) up to 0.55, preferably up to 2.5*(1−PVF) in one embodiment. Inembodiments the proppant PSD mode is from 100 to 2000 microns, the finesPSD mode from 1 to 20 microns, and/or the proppant PSD mode is from 18to 900 times larger than the fines PSD mode. In some embodiments, theslurry further comprises one or more intermediate PSD modes, preferablyselected from PSD modes from 2 to 60 times smaller than the proppant PSDmode, PSD modes from 1.1 to 60 times larger than the fines PSD mode, andcombinations thereof. In a particular embodiment, the intermediate PSDmodes can include a relatively larger PSD mode and a relatively smallerintermediate PSD mode, preferably wherein the larger intermediate PSDmode is from 2 to 15 times smaller than the proppant PSD mode and from1.25 to 15 times larger than the smaller intermediate PSD mode, andpreferably wherein the smaller intermediate mode is from 1.1 to 15 timeslarger than the fines PSD mode. In a further embodiment, the slurryfurther comprises a middle intermediate PSD mode from 1.5 to 4 timessmaller than the larger intermediate PSD mode and 1.25 to 2.5 timeslarger than the smaller PSD mode. In one embodiment, at least one of theintermediate PSD modes is degradable, preferably the larger intermediatePSD mode.

In a further embodiment, the slurry comprises a solids mixture in acarrier fluid, wherein the solids mixture comprises first, second, thirdand fourth volume-averaged particle size distribution (PSD) modes suchthat a packed volume fraction (PVF) of the solids mixture is greaterthan 0.75, preferably greater than 0.80; and a solids volume fraction(SVF) of the slurry is less than the PVF of the solids mixture; whereinthe first PSD mode is at least three times larger than the second PSDmode, the second PSD mode is larger than the third PSD mode, and thethird PSD mode is larger than the fourth PSD mode, and wherein at leastone of the second and third PSD modes is less than 3 times larger thanthe respective third or fourth PSD mode. The slurry can also include afifth PSD mode, wherein the fourth PSD mode is larger than the fifth PSDmode and preferably less than 3 times larger than the fifth PSD mode. Inone embodiment, the first PSD mode is from 3 to 10 (preferably about 5to about 7, more preferably about 5.4 to about 6.9, especially about 5.6to about 6.6 times larger than the second PSD mode) times larger thanthe second PSD mode, the second PSD mode is from 1.5 to 4 (preferablyfrom about 2 to about 2.4 times larger than the third PSD mode) timeslarger than the third PSD mode, the third PSD mode is at least 1.25(preferably up to about 2.5, more preferably about 1.8 or 1.9) timeslarger than the fourth PSD mode, and if the fifth PSD mode is present,the fourth PSD mode is at least 1.1 (preferably up to 2, more preferablyabout 1.6) times larger than the fifth PSD mode.

In one embodiment, the first PSD mode is from about 422 microns up toabout 853 microns (20/40 mesh), the second PSD mode is from about 60microns up to about 180 microns (preferably from about 100 microns up toabout 150 microns), the third PSD mode is from about 25 microns up toabout 70 microns (preferably from about 40 microns up to about 60microns), the fourth PSD mode is from about 1 micron up to about 40microns, and the fifth PSD mode, if present, is from about 1 micron upto about 25 microns. In another embodiment, the fifth PSD mode is atleast 1 micron and the first PSD mode is from about 422 microns (40mesh) up to about 853 microns (20 mesh). In an embodiment, the secondPSD mode comprises a total SVF from 5 to 30 percent (preferably from 10to 20 percent, more preferably from 10 to 15 percent), the third PSDmode comprises a total SVF from 3 to 20 percent (preferably from 3 to 10percent), the fourth PSD mode comprises a total SVF from 5 to 40 percent(preferably from 10 to 30 percent), based on a total SVF of the firstPSD mode, and the fifth PSD mode, if present, comprises a total SVF from1 to 40 percent, based on a total SVF of the first PSD mode.Additionally or alternatively, the second PSD mode comprises a total SVFfrom 5 to 30, preferably 10 to 20, percent of a total SVF of the firstPSD mode; the third PSD mode comprises a total SVF from 10 to 100,preferably 30 to 60, percent of the total SVF of the second PSD mode;the fourth PSD mode comprises a total SVF from 10 to 100, preferably 30to 80, percent of the total SVF of the third PSD mode; and if present,the fifth PSD mode comprises a total SVF from 10 to 500, preferably 100to 400, percent of the total SVF of the fourth PSD mode. In embodiments,the slurry can also comprise a fluid loss agent, a dispersant, and/orwherein at least one of the second, third, fourth or fifth PSD modescomprises a degradable material.

As is evident from the figures and text presented above, as well as theexamples below, a variety of embodiments are contemplated:

1. A method, comprising: combining a carrier fluid and a solids mixtureto form a preferably flowable slurry, wherein the solids mixturecomprises a plurality of volume-averaged particle size distribution(PSD) modes, wherein a first PSD mode comprises solids having avolume-average median size at least three times larger than thevolume-average median size of a second PSD mode such that a packedvolume fraction (PVF) of the solids mixture exceeds 0.75 or preferablyexceeds 0.8, and wherein the solids mixture, preferably the second PSDmode, comprises a degradable material and includes a reactive solid;circulating the slurry through a wellbore to form a pack of the solidsmixture having a PVF exceeding 0.75 or preferably exceeds 0.8 in one orboth of a fracture in a formation and an annulus between a screen andthe wellbore; degrading the degradable material in the pack to increaseporosity and permeability of the pack; and producing a reservoir fluidfrom the formation through the increased porosity pack.2. The method of embodiment 1, wherein the carrier fluid is a lowviscosity fluid free of viscosifier or comprising viscosifier in anamount less than 2.4 g of viscosifier per liter of carrier fluid (20lb/1000 gal).3. The method of embodiment 1 or 2, wherein the slurry is stable and hasa high particulate loading comprising at least 3.6 kg of the solidsmixture per liter of the carrier fluid (30 lb/gal).4. The method of embodiment 1, 2 or 3, wherein the first PSD modecomprises gravel and the second PSD mode comprises alumina trihydrateparticles, and wherein the degradation comprises changing a pH in thepack to solubilize the alumina trihydrate particles.5. The method of any one of embodiments 1 to 4, wherein the degradablematerial is soluble in basic fluids and the degradation comprisesincreasing a pH in the pack to dissolve the degradable material.6. The method of embodiment 5, wherein the degradable material isselected from the group consisting of amphoteric oxides, esters, coatedacids and combinations thereof.7. The method of any one of embodiments 1 to 6, wherein the solidsmixture comprises base or base precursor.8. The method of embodiment 7, wherein the base or base precursor issparingly soluble or encapsulated.9. The method of embodiment 7 or 8, wherein the base is selected fromthe group consisting of alkali metal and ammonium hydroxides, organicamines, urea, substituted urea and combinations thereof.10. The method of any one of embodiments 1 to 9, comprising contactingthe pack with a basic aqueous solution.11. The method of any one of embodiments 1 to 4, wherein the degradablematerial is soluble in acidic fluids and the degradation comprisesdecreasing a pH in the pack to dissolve the degradable material.12. The method of embodiment 1 or 11, wherein the degradable material isselected from the group consisting of oxides and hydroxides of aluminum,zinc, tin, lead, boron, silicon and iron; carbonates, sulfates, oxidesand hydroxides of calcium, magnesium and barium; and combinationsthereof.13. The method of embodiment 1, 11 or 12, wherein the solids mixturecomprises an acid or acid precursor.14. The method of embodiment 13, wherein the acid or acid precursor issparingly soluble or encapsulated.15. The method of embodiment 13 or 14, wherein the acid precursor isselected from the group consisting of hydrolyzable esters, acidanhydrides, acid sulfonates, acid halides and combinations thereof.16. The method of any one of embodiments 1 or 11 to 15, comprisingcontacting the pack with an acidic aqueous solution.17. The method of any one of embodiments 11 to 16, wherein the secondPSD mode comprises an encapsulated water- or oil-soluble solid, and thedegradation comprises de-encapsulating the soluble solid.18. The method of any one of embodiments 11 to 17, wherein the secondPSD mode comprises a water-soluble solid and the carrier fluid comprisesa saturated aqueous solution of the water-soluble solid, and thedegradation comprises contacting the pack with an undersaturated aqueousmedium.19. The method of any one of embodiments 11 to 17, wherein the secondPSD mode comprises a water-soluble solid, and the carrier fluidcomprises an invert oil emulsion wherein the water-soluble solid isdispersed in an oil phase, and the degradation comprises breaking theemulsion to dissolve the water-soluble solid in an aqueous medium.20. The method of embodiment 19, comprising contacting the pack with ade-emulsifier to break the emulsion.21. The method of embodiment 19 or 20, comprising contacting the packwith a pH control agent to break the emulsion.22. The method of embodiment 21, wherein the pH control agent isselected from the group consisting of monoesters, polyesters, weakacids, weak bases, urea, urea derivatives and combinations thereof.23. The method of any one of embodiments 1 to 22, wherein the degradablematerial comprises a soluble material.24. The method of embodiment 23, wherein the carrier fluid is saturatedwith respect to the soluble material.25. The method of embodiment 23 or 24, wherein the soluble materialcomprises salt and the carrier fluid comprises brine.26. A composition, comprising: a carrier fluid and a solids mixturecombined to form a flowable slurry, wherein the solids mixture comprisesa plurality of volume-averaged particle size distribution (PSD) modes,wherein a first PSD mode comprises solids having a volume-average mediansize at least three times larger than the volume-average median size ofa second PSD mode such that a packed volume fraction (PVF) of the solidsmixture exceeds 0.75 or preferably exceeds 0.8, and wherein the solidsmixture, preferably the second PSD mode, comprises a degradable materialand includes a reactive solid.27. The composition of embodiment 26, wherein the carrier fluid is a lowviscosity fluid free of viscosifier or comprising viscosifier in anamount less than 2.4 g of viscosifier per liter of carrier fluid (20lb/1000 gal).28. The composition of embodiment 26 or 27, wherein the slurry is stableand has a high particulate loading comprising at least 3.6 kg of thesolids mixture per liter of the carrier fluid (30 lb/gal).29. The composition of embodiment 26, 27 or 28, wherein the first PSDmode comprises gravel and the second PSD mode comprises aluminatrihydrate particles.30. The composition of any one of embodiments 26 to 30, wherein thedegradable material is soluble in basic fluids.31. The composition of embodiment 30, wherein the degradable material isselected from the group consisting of amphoteric oxides, esters, coatedacids and combinations thereof.32. The composition of any one of embodiments 26 to 31, wherein thesolids mixture comprises base or base precursor.33. The composition of embodiment 32, wherein the base or base precursoris sparingly soluble or encapsulated.34. The composition of embodiment 32 or 33, wherein the base is selectedfrom the group consisting of alkali metal and ammonium hydroxides,organic amines, urea, substituted urea and combinations thereof.35. The composition of any one of embodiments 26 to 29, wherein thedegradable material is soluble in acidic fluids.36. The composition of any one of embodiments 26 to 30 or 35, whereinthe degradable material is selected from the group consisting of oxidesand hydroxides of aluminum, zinc, tin, lead, boron, silicon and iron;carbonates, sulfates, oxides and hydroxides of calcium, magnesium andbarium; and combinations thereof.37. The composition of any one of embodiments 26 to 30 or 35 to 36,wherein the solids mixture comprises an acid or acid precursor.38. The composition of embodiment 37, wherein the acid or acid precursoris sparingly soluble or encapsulated.39. The composition of embodiment 37 or 38, wherein the acid precursoris selected from the group consisting of hydrolyzable esters, acidanhydrides, acid sulfonates, acid halides and combinations thereof.40. The composition of any one of embodiments 26 to 39, wherein thesecond PSD mode comprises an encapsulated water- or oil-soluble solid.41. The composition of any one of embodiments 26 to 39, wherein thesecond PSD mode comprises a water-soluble solid and the carrier fluidcomprises a saturated aqueous solution of the water-soluble solid.42. The composition of embodiment 40 or 41, wherein the soluble materialcomprises salt and the carrier fluid comprises brine.43. The composition of any one of embodiments 26 to 39, wherein thesecond PSD mode comprises a water-soluble solid, and the carrier fluidcomprises an invert oil emulsion wherein the water-soluble solid isdispersed in an oil phase.44. A method, comprising: combining a carrier fluid and a solids mixtureto form a preferably flowable slurry, wherein the solids mixturecomprises a plurality of volume-averaged particle size distribution(PSD) modes such that a packed volume fraction (PVF) of the solidsmixture exceeds 0.75, or preferably exceeds 0.8; contacting a screenwith a fluid comprising leak-off control agent to form a bridge on thescreen to inhibit fluid entry; positioning the screen in a wellbore andcirculating the slurry through the wellbore in any order such that thesolids mixture is deposited between the screen and the wellbore;converting the deposited solids mixture into a gravel pack to increaseporosity and permeability; removing the bridge from the screen; andproducing a reservoir fluid from the formation through the gravel packand the screen.45. The method of embodiment 44, wherein the slurry comprises theleak-off control agent and the bridge is formed on the screen during thecirculation of the slurry.46. The method of embodiment 45, wherein the solids mixture comprisesthree PSD modes to form the bridge on the screen, wherein a first amountof particulates have a first PSD, a second amount of particulates have asecond PSD, and a third amount of particulates have a third PSD, whereinthe first PSD is larger than the second PSD, and wherein second PSD islarger than the third PSD.47. The method of embodiment 46, wherein the first amount ofparticulates comprises 40/80 mesh (178-422 microns) gravel.48. The method of embodiment 46 or 47, wherein the first PSD is smallerthan 40 mesh (422 microns).49. The method of any one of embodiments 44 to 48, wherein the solidsmixture comprises three PSD modes, wherein a first amount ofparticulates have a first PSD, a second amount of particulates have asecond PSD, and a third amount of particulates have a third PSD, whereinthe first PSD is from two to ten times larger than the second PSD, andwherein second PSD is from three to ten times larger than the third PSD.50. The method of any one of embodiments 44 to 49, wherein the leak-offcontrol fluid comprises a spacer fluid introduced into the wellbore.51. The method of embodiment 50, wherein the slurry is circulatedthrough the wellbore before the screen is positioned in the wellbore,wherein the spacer fluid is positioned in the wellbore above the slurry,and wherein the screen is passed through the spacer fluid in thewellbore and then stabbed into the slurry.52. The method of embodiment 50, wherein the screen is positioned in thewellbore before the slurry is circulated into an annulus between thescreen and the wellbore, and wherein the spacer fluid is circulated intothe annulus ahead of the slurry.53. The method of any one of embodiments 50 to 52, wherein the spacerfluid and slurry are sequentially pumped through a flow passage in thescreen to a bottom end of the screen and into the annulus.54. A method, comprising: combining a carrier fluid, a first amount ofparticulates, a second amount of particulates, and a third amount ofparticulates into a slurry; wherein the first amount of particulateshave a first average size distribution, the second amount ofparticulates have a second average size distribution, and the thirdamount of particulates have a third average size distribution, whereinthe first average size distribution is at least three times larger thanthe second average size distribution, and wherein the second averagesize distribution is larger than the third average size distribution;wherein at least one of the second amount of particulates and the thirdamount of particulates comprise a degradable material; positioning ascreen in a wellbore in a subterranean formation and circulating theslurry through the wellbore in any order such that the first amount ofparticulates, the second amount of particulates, and the third amount ofparticulates form a bridge on a surface of the screen to inhibit fluidentry and a solids pack in an annulus between the screen surface and asurface of the wellbore; and selectively removing from the first amountof particulates at least a portion of the particulates selected from thesecond amount of particulates, the third amount of particulates and acombination thereof, to increase porosity and permeability in the bridgeand the solids pack for fluid flow across the annulus and through thescreen.55. The method of any one of embodiments 1 to 25 or 54, wherein thescreen is disposed into the wellbore before the slurry is circulated.56. The method of any one of embodiments 1 to 25 or 54, wherein theslurry is circulated into the wellbore before the screen is disposed inthe wellbore.57. The method of any one of embodiments 54 to 56, wherein the firstamount of particulates and the second amount of particulates have acombined dry packing volume fraction greater than about 0.75, preferablygreater than 0.8.58. The method of any one of embodiments 54 to 57, wherein the slurry iscombined prior to circulation in the wellbore.59. The method of any one of embodiments 54 to 57, wherein a sum of allparticulates in the slurry exceeds thirty pounds per gallon of carrierfluid.60. The method of any one of embodiments 54 to 57, wherein the secondaverage size distribution is at least three times larger than the thirdaverage size distribution.61. The method of embodiment 60, wherein the total solids volume of thethird amount of particulates is greater than the total solids volume ofthe second amount of particulates.62. The method of any one of embodiments 54 to 61, wherein the slurryfurther includes a fourth amount of particulates having a fourth averagesize distribution, and wherein the third average size distribution islarger than the fourth average size distribution.63. The method of embodiment 62, wherein the slurry further includes afifth amount of particulates having a fifth average size distribution,and wherein the fourth average size distribution is larger than thefifth average size distribution.64. The method of any one of embodiments 54 to 63, wherein the firstaverage size distribution is between about six and ten times larger thanthe second average size distribution.65. The method of any one of embodiments 54 to 64, wherein the secondaverage size distribution is between about 1.5 and 15 times larger thanthe third average size distribution.66. The method of embodiment 65, wherein the slurry further includes afourth amount of particulates having a fourth average size distribution,and wherein the third average size distribution is between about 1.25and 15 times larger than the fourth average size distribution.67. The method of embodiment 66, wherein the slurry further includes afifth amount of particulates having a fifth average size distribution,and wherein the fourth average size distribution is between about 1.1and 15 times larger than the fifth average size distribution.68. A method, comprising: combining a carrier fluid, a first amount ofparticulates, a second amount of particulates, a third amount ofparticulates and a fourth amount of particulates into a slurry; whereinthe first amount of particulates have a first average size distribution,the second amount of particulates have a second average sizedistribution, the third amount of particulates have a third average sizedistribution, and the fourth amount of particulates have a fourthaverage size distribution, wherein the first average size distributionis at least three times larger than the second average sizedistribution, wherein the second average size distribution is at leastthree times larger than the third average size distribution, and whereinthe third average size distribution is at least three times larger thanthe fourth average size distribution; positioning a screen in a wellborein a subterranean formation and circulating the slurry through thewellbore in any order such that the first amount of particulates, thesecond amount of particulates, and the third amount of particulates forma bridge on a surface of the screen to inhibit fluid entry and a solidspack in an annulus between the screen surface and a surface of thewellbore; selectively removing from the first amount of particulates atleast a portion of the particulates selected from the second amount ofparticulates, the third amount of particulates, the fourth amount ofparticulates, and combinations thereof, to increase porosity andpermeability in the bridge and the solids pack for fluid flow across theannulus and through the screen.69. The method of embodiment 68, wherein the first amount ofparticulates comprises gravel.70. The method of embodiment 68 or 69, wherein the first average sizedistribution is 40 mesh (422 μm) or larger.71. The method of any one of embodiments 68 to 70, wherein the firstamount of particulates comprises 20/40 mesh gravel.72. The method of any one of embodiments 68 to 71, wherein the slurryfurther comprises a fifth amount of particulates having a fifth averageparticle size distribution, wherein the fourth average particle sizedistribution is at least three times larger than the fifth averageparticle size distribution.73. The method of any one of embodiments 68 to 72, wherein the firstaverage size distribution is between 20 and 40 mesh (422-853 μm), thesecond average size distribution is from 140 μm to 280 μm, the thirdaverage size distribution is from 15 to 65 μm, and the fourth averagesize distribution is from 1 to 10 μm.74. The method of any one of embodiments 68 to 73, wherein the firstaverage size distribution is from 3 to 15 times larger than the secondaverage size distribution, wherein the second average size distributionis from 3 to 15 times larger than the third average size distribution,and wherein the third average size distribution is from 3 to 15 timeslarger than the fourth average size distribution.75. The method of any one of embodiments 68 to 74, wherein at least oneof the second amount of particulates and the third amount ofparticulates comprise a degradable material.76. The method of any one of embodiments 68 to 75, wherein the slurryfurther comprises a fluid loss agent to inhibit leak-off from theslurry.77. The method of embodiment 76, wherein the fluid loss agent isselected from the group consisting of: latex dispersions, water solublepolymers, submicron particulates, particulates with an aspect ratiohigher than 6, and combinations thereof.78. The method of embodiment 76 or 77, wherein the fluid loss agentcomprises crosslinked polyvinyl alcohol microgel.79. The method of any one of embodiments 76 to 78, wherein the fluidloss agent further comprises AMPS.80. The method of any one of embodiments 68 to 79, wherein the slurrycomprises a solids volume fraction (SVF) from 0.5 to 0.75.81. The method of any one of embodiments 68 to 80, wherein the totalparticulates in the slurry have a packed volume fraction (PVF) greaterthan the SVF.82. The method of any one of embodiments 1 to 25 or 44 to 81, whereinthe slurry is circulated in a horizontal portion of the wellbore fromtoe to heel.83. The method of any one of embodiments 1 to 25 or 44 to 82, whereinthe slurry is circulated in the wellbore at a pressure less than thefracture pressure.84. The method of any one of embodiments 1 to 25 or 44 to 83, whereinthe slurry is circulated in the wellbore at a rate less than 800 L/min(5 BPM).85. The method of any one of embodiments 1 to 25 or 44 to 84, whereinthe slurry is circulated in the wellbore through a washpipe, wherein ascreen-wellbore annulus has a radial thickness relatively less than aradial thickness of a washpipe-screen annulus.86. A system, comprising: a slurry comprising a carrier fluid suspendinga first amount of particulates, a second amount of particulates, and athird amount of particulates; wherein the first amount of particulateshave a first average size distribution, the second amount ofparticulates have a second average size distribution, and the thirdamount of particulates have a third average size distribution; whereinthe first average size distribution is at least three times larger thanthe second average size distribution, and wherein the second averagesize distribution is at least three times larger than the third averagesize distribution; wherein at least one of the second amount ofparticulates and the third amount of particulates comprise a degradablematerial; and a tubing string and a slurry pump to position a screen andcirculate the slurry in a wellbore in a subterranean formation in anyorder such that the first amount of particulates, the second amount ofparticulates, and the third amount of particulates form a bridge on asurface of the screen and a solids pack in an annulus between the screensurface and a surface of the wellbore, and wherein the degradablematerial can be selectively removed from the first amount ofparticulates to increase porosity and permeability in the solids packfor fluid flow across the annulus and through the screen.87. The system of embodiment 86, wherein the first amount ofparticulates and the second amount of particulates have a combined drypacking volume fraction greater than about 0.75, preferably greater than0.80.88. The system of embodiment 86 or 87, wherein a sum of all particulatesin the slurry exceeds thirty pounds per gallon of carrier fluid.89. The system of any one of embodiments 86 to 88, wherein the totalsolids volume of the third amount of particulates is greater than thetotal solids volume of the second amount of particulates.90. The system of any one of embodiments 86 to 89, wherein the slurryfurther includes a fourth amount of particulates having a fourth averagesize distribution, and wherein the third average size distribution islarger than the fourth average size distribution.91. The system of embodiment 90, wherein the slurry further includes afifth amount of particulates having a fifth average size distribution,and wherein the fourth average size distribution is larger than thefifth average size distribution.92. The system of any one of embodiments 86 to 91, wherein the firstaverage size distribution is between about six and ten times larger thanthe second average size distribution.93. A method, comprising: combining a carrier fluid, a solids mixtureand a stability additive to form a slurry, wherein the solids mixturecomprises a plurality of volume-averaged particle size distribution(PSD) modes such that a packed volume fraction (PVF) exceeds 0.75,preferably exceeds 0.8, wherein the slurry comprises a solids volumefraction (SVF) less than the PVF of the solids mixture; circulating theslurry into a wellbore to deposit the slurry downhole; terminating theslurry circulation for a period of time, wherein the stability additiveinhibits settling of the solids mixture; and thereafter circulating thedeposited slurry in contact with a surface of a screen.94. The method of embodiment 93, wherein the stability additivecomprises colloidal particles.95. The method of embodiment 94, wherein the colloidal particles areselected from the group consisting of γ-alumina, MgO, γ-Fe2O3, andcombinations thereof.96. The method of any one of embodiments 93 to 95, wherein the stabilityadditive comprises hydratable polymer particles.97. The method of embodiment 96, wherein the polymer particles have ahydration temperature above 60° C.98. The method of embodiment 96 or 97, wherein the polymer particlescomprise heteropolysaccharide.99. The method of embodiment 96, 97 or 98, wherein the polymer particlescomprise gellan gum.100. The method of any one of embodiments 93 to 99, wherein thestability additive comprises stabilizing particles having an aspectratio above 6.101. The method of embodiment 100, wherein the stabilizing particleshaving an aspect ratio above 6 are degradable.102. The method of embodiment 100 or 101, wherein the stabilizingparticles having an aspect ratio above 6 comprise flakes, fibers or acombination thereof comprising a polymer or copolymer of lactic acid,glycolic acid, or the combination thereof.103. The method of any one of embodiments 93 to 102, wherein thecirculation of the deposited slurry in contact with the surface of thescreen comprises stabbing the screen into the deposited slurry.104. The method of any one of embodiments 93 to 103, wherein the slurrycirculation is terminated to trip a workstring from the wellbore andtrip the screen into the wellbore.105. The method of any one of embodiments 93 to 104, wherein the SVF isfrom 0.5 to 0.75, preferably from 0.55 to 0.7, preferably from 0.56 to0.68, preferably from 0.58 to 0.66.106. The method of any one of embodiments 93 to 105, wherein one of thePSD modes comprises gravel.107. The method of any one of embodiments 93 to 106, wherein the solidsmixture is trimodal.108. The method of any one of embodiments 93 to 106, wherein the solidsmixture is tetramodal.109. The method of any one of embodiments 93 to 106, wherein the solidsmixture is pentamodal.110. The method of any one of embodiments 93 to 109, further comprisingforming the solids mixture in the slurry into a pack in an annulusbetween the screen and the wellbore.111. The method of embodiment 110, further comprising converting thepack into a permeable gravel pack.112. A slurry, comprising: a solids mixture comprising a plurality ofvolume-averaged particle size distribution (PSD) modes such that apacked volume fraction (PVF) exceeds 0.75, preferably exceeds 0.8; acarrier fluid in an amount to provide a solids volume fraction (SVF)less than the PVF of the solids mixture; and a stability additive toinhibit settling of the solids mixture.113. The slurry of embodiment 112, wherein the stability additivecomprises colloidal particles.114. The slurry of embodiment 113, wherein the colloidal particles areselected from the group consisting of γ-alumina, MgO, γ-Fe2O3, andcombinations thereof.115. The slurry of any one of embodiments 112, 113 or 114, wherein thestability additive comprises hydratable polymer particles.116. The slurry of embodiment 115, wherein the polymer particles have ahydration temperature above 60° C.117. The slurry of embodiment 115 or 116, wherein the polymer particlescomprise heteropolysaccharide.118. The slurry of any one of embodiments 115, 116 or 117, wherein thepolymer particles comprise gellan gum.119. The slurry of any one of embodiments 112 to 118, wherein thestability additive comprises stabilizing particles having an aspectratio above 6.120. The slurry of embodiment 119, wherein the stabilizing particleshaving an aspect ratio above 6 are degradable.121. The slurry of embodiment 119 or 120, wherein the stabilizingparticles having an aspect ratio above 6 comprise flakes comprising apolymer or copolymer of lactic acid, glycolic acid, or the combinationthereof.122. The slurry of any one of embodiments 112 to 121, wherein the SVF isfrom 0.5 to 0.75, preferably from 0.55 to 0.7, preferably from 0.56 to0.68, preferably from 0.58 to 0.66.123. The slurry of any one of embodiments 112 to 122, wherein one of thePSD modes comprises gravel.124. The slurry of any one of embodiments 112 to 123, wherein the solidsmixture is trimodal.125. The slurry of any one of embodiments 112 to 123, wherein the solidsmixture is tetramodal.126. The slurry of any one of embodiments 112 to 123, wherein the solidsmixture is pentamodal.127. The slurry of any one of embodiments 112 to 126, wherein the slurryis stable and flowable for at least 48 hours.128. A method to stabilize a slurry comprising a solids mixture in acarrier fluid, wherein the solids mixture comprises from three to fivevolume-averaged particle size distribution (PSD) modes such that apacked volume fraction (PVF) exceeds 0.75, or preferably exceeds 0.8,and wherein the slurry comprises a solids volume fraction (SVF) lessthan the PVF of the solids mixture, comprising: introducing a stabilityadditive into the slurry, wherein the stability additive is selectedfrom the group consisting of colloidal particles, hydratable polymerparticles, particles having an aspect ratio above 6, and combinationsthereof.129. The method of embodiment 128, wherein the stability additivecomprises colloidal particles selected from the group consisting ofγ-alumina, MgO, γ-Fe2O3, and combinations thereof.130. The method of embodiment 128 or 129, wherein the stability additivecomprises hydratable polymer particles having a hydration temperatureabove 60° C.131. The method of embodiment 128, 129 or 130, wherein the stabilityadditive comprises heteropolysaccharide.132. The method of any one of embodiments 128 to 131, wherein thestability additive comprises gellan gum.133. The method of any one of embodiments 128 to 132, wherein thestability additive comprises stabilizing particles having an aspectratio above 6, wherein the stabilizing particles are degradable.134. The method of embodiment 133, wherein the stabilizing particleshaving an aspect ratio above 6 comprise flakes comprising a polymer orcopolymer of lactic acid, glycolic acid, or the combination thereof.135. The method of any one of embodiments 128 to 134, wherein the slurryhas an SVF from 0.5 to 0.75, preferably from 0.55 to 0.7, preferablyfrom 0.56 to 0.68, preferably from 0.58 to 0.66.136. The method of any one of embodiments 128 to 135, wherein one of thePSD modes comprises gravel.137. The method of any one of embodiments 128 to 136, wherein the slurryis stable and flowable for at least 48 hours following the introductionof the stabilizing additive into the slurry.138. A method, comprising: positioning a generally cylindrical screen ina wellbore to define an annulus between the screen and the wellbore; andpassing a slurry comprising a carrier fluid and a solids mixture throughthe wellbore, through a passage within the screen to a bottom end of thescreen and into the annulus to pack the solids mixture onto an outersurface of the screen; wherein the solids mixture comprises at least twovolume-averaged particle size distribution (PSD) modes, wherein a firstPSD mode comprises solids having a volume-average median size at leastthree times larger than the volume-average median size of a second PSDmode such that a packed volume fraction (PVF) of the solids mixtureexceeds 0.75 or preferably exceeds 0.8.139. The method of embodiment 138, wherein the screen positioningemploys a workstring comprising drill pipe, packer assembly, and awashpipe, and further comprising connecting the washpipe to a bottom endof the screen, pumping the slurry down the drill pipe through thewashpipe and out of the bottom end into the annulus, and furthercomprising, after pumping the slurry into the annulus, setting thepacker and removing the washpipe.140. The method of embodiment 138 or 139, wherein the annulus has aradial thickness (wellbore inside radius minus screen outside radius)less than 25 mm.141. The method of any one of embodiments 138 to 140, wherein the slurryis circulated in the annulus at a pressure less than the fracturepressure, preferably at a rate of less than 800 L/min (5 BPM).142. The method of embodiment 138, wherein the screen positioningemploys a workstring comprising drill pipe, packer assembly, washpipe,the screen and an end cap comprising a port to allow the washpipe toconnect to a bottom of the assembly, and further comprising setting thepacker, pumping the slurry down the drill pipe through the washpipe andout of the bottom of the assembly into the annulus to build up pressurein the annulus greater than a fracture pressure to fracture theformation, and thereafter removing the drill pipe and the washpipe fromthe wellbore.143. The method of embodiment 138, wherein the screen positioningemploys a production assembly comprising production tubing, the screenand a packer, wherein the screen is coated with a degradable material toinhibit inflow, wherein following the screen positioning, the slurry ispumped down the production tubing through the central flow passage, outof the distal end into the annulus, and further comprising, afterpumping the slurry into the annulus, setting the packer, degrading thedegradable material for inflow into the screen and producing reservoirfluid through the production tubing.144. The method of embodiment 138, wherein the screen positioningemploys a production assembly comprising production tubing, the screenand a packer, wherein the screen contains a degradable material within abase pipe to inhibit inflow, wherein following the screen positioning,the slurry is pumped down the production tubing through the central flowpassage, out of the distal end into the annulus, and further comprising,after pumping the slurry into the annulus, setting the packer, degradingthe degradable material for inflow and producing reservoir fluid throughthe production tubing.145. The method of embodiment 138, wherein the screen positioningemploys a production assembly comprising production tubing, the screen,a packer, and a mechanical inflow device to selectively inhibit or allowinflow, wherein following the screen positioning, the slurry is pumpeddown the production tubing through the central flow passage, out of thedistal end into the annulus, and further comprising, after pumping theslurry into the annulus, setting the packer, activating the inflowdevice to allow inflow into the screen and producing reservoir fluidthrough the production tubing.146. The method of embodiment 145 wherein the inflow device is remotelyactivated.147. The method of embodiment 145 0r 146, wherein the inflow device isactivated by a timing device at a prescribed time after the productionassembly is run in hole.148. The method of any one of embodiments 138 to 147, further comprisingsetting a chemical packer in an annulus between the wellbore and atubing connected to the screen.149. The method of embodiment 148, wherein the chemical packer is runahead of the slurry.150. The method of any one of embodiments 138 to 149, further comprisingsetting a plurality of spaced chemical packers in the screen-wellboreannulus and optionally in an annulus between the wellbore and a tubingconnected to the screen, to create zonal isolation.151. The method of any one of embodiments 148 to 150, wherein thechemical packer is introduced to the tubing-wellbore annulus through adiversion port above the screen.152. The method of embodiment 138, wherein the screen positioningemploys a drilling assembly comprising a drill string, the screen, aliner packer and a drilling and measurement assembly comprising a drillbit, the screen positioning comprising drilling a final length of holeto place the screen, the slurry circulation comprising pumping theslurry through the drilling assembly out of the drill bit and into theannulus, and further comprising, after pumping the slurry into theannulus, setting the liner packer, removing the drill string andabandoning the bit downhole.153. The method of embodiment 152, further comprising pumping a pluggingmaterial to follow the slurry and seal off a bottom of the wellbore.154. The method of embodiment 138, wherein the screen positioningemploys a drilling assembly comprising a drill string, the screen, aliner packer and a drilling and measurement assembly comprising a drillbit, the screen positioning comprising drilling a final length of holeto place the screen, and further comprising setting the packer, pumpingthe slurry through the drilling assembly out of the drill bit and intothe annulus to build up pressure in the annulus greater than a fracturepressure to fracture the formation, removing the drill string andabandoning the bit downhole.155. The method of embodiment 138, wherein the screen positioningemploys a drilling assembly comprising a drill string, the screen and adrilling and measurement assembly comprising a drill bit, the screenpositioning comprising drilling a final length of hole to place thescreen, the slurry circulation comprising pumping a chemical packerahead of the slurry through the drilling assembly out of the drill bitand into the annulus, and further comprising, after pumping the chemicalpacker and the slurry into the annulus, setting the chemical packer,removing the drill string and abandoning the bit downhole.156. The method of embodiment 155, further comprising pumping cementahead of the chemical packer to place cement around any free casing.157. The method of any one of embodiments 138 to 156, further comprisingtransforming the packed solids mixture into a permeable gravel pack.158. A method, comprising: combining a carrier fluid and a solidsmixture to form a slurry, wherein the solids mixture comprises aplurality of volume-averaged particle size distribution (PSD) modes suchthat a packed volume fraction (PVF) exceeds 0.75, preferably exceeds0.8, wherein the solids mixture comprises at least a proppant PSD modeand a fines PSD mode; circulating the slurry through a wellbore to forma proppant pack from depositing the solids mixture in one or both of afracture in a formation and an annulus between a screen and thewellbore; contacting fines in the pack with a dispersant; passing fluidthrough the pack to remove fines from the pack.159. The method of embodiment 158, wherein the dispersant is present inthe slurry.160. The method of embodiment 158, wherein contacting the fines with thedispersant comprises displacing the carrier fluid from the proppant packwith another fluid comprising the dispersant.161. The method of any one of embodiments 158 to 160, wherein contactingthe fines with the dispersant comprises circulating a fluid comprisingthe dispersant in the wellbore after forming the pack.162. The method of any one of embodiments 158 to 161, wherein contactingthe fines with the dispersant comprises spotting a fluid comprising thedispersant in contact with the pack after forming the pack.163. The method of any one of embodiments 158 to 162, wherein thedispersant comprises a polyelectrolyte.164. The method of any one of embodiments 158 to 163, wherein thedispersant comprises polysulfonate, polycarboxylate or a combinationthereof.165. The method of any one of embodiments 158 to 164, wherein thedispersant comprises lignosulfonate, polymelamine sulfonate, polystyrenesulfonate, polynaphthalene sulfonate or a combination thereof.166. The method of any one of embodiments 158 to 165, wherein thedispersant comprises polynaphthalene sulfonate.166A. The method of any one of embodiments 158 to 166, wherein thedispersant comprises polyacrylate having a weight average molecularweight less than 10,000 Daltons167. The method of any one of embodiments 158 to 166A, wherein thedispersant comprises an anionic, cationic, amphoteric or zwitterionicsurfactant.168. The method of any one of embodiments 158 to 167, wherein thedispersant comprises a nonionic surfactant and preferably the carrierfluid comprises brine.169. The method of any one of embodiments 158 to 168, wherein a weightratio of dispersant to fines is from about 1:500 to about 10:90.170. The method of any one of embodiments 158 to 169, wherein the finescomprise silica.171. The method of any one of embodiments 158 to 170, wherein the finescomprise calcium carbonate.172. The method of any one of embodiments 158 to 171, wherein the finesare agglomerated in the slurry.173. The method of any one of embodiments 158 to 172, wherein the slurrycomprises a volume fraction of solids of from about 0.45 up to the PVF.174. The method of any one of embodiments 158 to 173, wherein the slurrycomprises a volume fraction of carrier fluid from (1−PVF) to 0.55,preferably to 2.5*(1−PVF).175. The method of any one of embodiments 158 to 174, wherein theproppant PSD mode is from 100 to 2000 microns and the fines PSD mode isfrom 1 to 20 microns.176. The method of any one of embodiments 158 to 175, wherein theproppant PSD mode is from 18 to 900 times larger than the fines PSDmode.177. The method of any one of embodiments 158 to 176, wherein the slurryfurther comprises one or more intermediate PSD modes selected from thegroup consisting of PSD modes from 2 to 60 times smaller than theproppant PSD mode, PSD modes from 1.1 to 60 times larger than the finesPSD mode, and combinations thereof.178. The method of embodiment 177, wherein at least one of theintermediate PSD modes is degradable, and further comprising degradingthe at least one degradable intermediate PSD mode after forming thepack.179. The method of any one of embodiments 177 to 178, wherein theintermediate PSD modes include a relatively larger PSD mode and arelatively smaller intermediate PSD mode, wherein the largerintermediate PSD mode is from 2 to 15 times smaller than the proppantPSD mode and from 1.25 to 15 times larger than the smaller intermediatePSD mode, and wherein the smaller intermediate mode is from 1.1 to 15times larger than the fines PSD mode.179A. The method of embodiment 179, further comprising a middleintermediate PSD mode from 1.5 to 4 times smaller than the largerintermediate PSD mode and 1.25 to 2.5 times larger than the smaller PSDmode.180. The method of embodiment 179 or 179A, wherein the largerintermediate PSD mode is degradable, and further comprising degradingthe larger intermediate PSD mode after forming the pack.181. The method of any one of embodiments 158 to 180, wherein at least70 percent of the fines are removed from the pack.182. The method of any one of embodiments 158 to 181, further comprisingproducing reservoir fluid through the cleaned pack into the wellbore.183. The method of any one of embodiments 158 to 182, comprising gravelpacking wherein the slurry is circulated in the wellbore at a rate lessthan about 800 L/min (5 BPM), preferably to avoid fracturing theformation.184. The method of any one of embodiments 158 to 183, wherein thecarrier fluid is a low viscosity fluid free of viscosifier or comprisingviscosifier in an amount less than 2.4 g of viscosifier per liter ofcarrier fluid (20 lb/1000 gal).185. A system, comprising: a well bore in fluid communication with asubterranean formation; a gravel packing slurry comprising a carrierfluid and a solids mixture, wherein the solids mixture comprises aplurality of volume-averaged particle size distribution (PSD) modes suchthat a packed volume fraction (PVF) exceeds 0.75, preferably exceeds0.8, wherein the solids mixture comprises at least a proppant PSD modeand a fines PSD mode; a pump to circulate the slurry in the wellbore todeposit the solids mixture and form a proppant pack in one or both of afracture in the formation and an annulus between a screen and theformation; and a dispersant source effective to facilitate finesflowback from the pack.186. The system of embodiment 185, wherein the dispersant is present inthe slurry.187. The system of embodiment 185 or 186, wherein the dispersant sourcecomprises a dispersant circulation or spotting fluid.188. The system of any one of embodiments 185 to 187, wherein thedispersant comprises a polyelectrolyte.189. The system of any one of embodiments 185 to 188, wherein thedispersant comprises polysulfonate, polycarboxylate or a combinationthereof.190. The system of any one of embodiments 185 to 189, wherein thedispersant comprises a lignosulfonate, polymelamine sulfonate,polystyrene sulfonate, polynaphthalene sulfonate or a combinationthereof.191. The system of any one of embodiments 185 to 190, wherein thedispersant comprises polynaphthalene sulfonate.191A. The system of any one of embodiments 185 to 191, wherein thedispersant comprises polyacrylate having a weight average molecularweight less than 10,000 Daltons192. The system of any one of embodiments 185 to 191A, wherein thedispersant comprises an anionic, cationic, amphoteric or zwitterionicsurfactant.193. The system of any one of embodiments 185 to 192, wherein thedispersant comprises a nonionic surfactant and preferably the carrierfluid comprises brine.194. The system of any one of embodiments 185 to 193, wherein a weightratio of dispersant to fines is from about 1:500 to about 10:90.195. The system of any one of embodiments 185 to 194, wherein the finescomprise silica.196. The system of any one of embodiments 185 to 195, wherein the finescomprise calcium carbonate.197. The system of any one of embodiments 185 to 196, wherein the finesare agglomerated in the slurry.198. The system of any one of embodiments 185 to 197, wherein the slurrycomprises a volume fraction of solids of from about 0.45 up to the PVF.199. The system of any one of embodiments 185 to 198, wherein the slurrycomprises a volume fraction of carrier fluid from (1−PVF) to 0.55,preferably up to 2.5*(1−PVF).200. The system of any one of embodiments 185 to 199, wherein theproppant PSD mode is from 100 to 2000 microns and the fines PSD mode isfrom 1 to 20 microns.201. The system of any one of embodiments 185 to 200, wherein theproppant PSD mode is from 18 to 900 times larger than the fines PSDmode.202. The system of any one of embodiments 185 to 201, wherein the slurryfurther comprises one or more intermediate PSD modes selected from thegroup consisting of: PSD modes from 2 to 60 times smaller than theproppant PSD mode, PSD modes from 1.1 to 60 times larger than the finesPSD mode, and combinations thereof.203. The system of embodiment 202, wherein at least one of theintermediate PSD modes is degradable.204. The system of embodiment 202 or 203, wherein the intermediate PSDmodes include a relatively larger intermediate PSD mode and a relativelysmaller intermediate PSD mode, preferably wherein the largerintermediate PSD mode is from 2 to 15 times smaller than the proppantPSD mode and from 1.25 to 15 times larger than the smaller intermediatePSD mode, and wherein the smaller intermediate mode is from 1.1 to 15times larger than the fines PSD mode.205. The system of embodiment 204, further comprising a middleintermediate PSD mode from 1.5 to 4 times smaller than the largerintermediate PSD mode and 1.25 to 2.5 times larger than the smaller PSDmode.206. The system of embodiment 204 or 205, wherein the relatively largerintermediate PSD mode is degradable.207. The system of any one of embodiments 185 to 206, wherein thecarrier fluid is a low viscosity fluid free of viscosifier or comprisingviscosifier in an amount less than 2.4 g of viscosifier per liter ofcarrier fluid (20 lb/1000 gal).208. A slurry, comprising: a solids mixture in a carrier fluid, whereinthe solids mixture comprises first, second, third and fourthvolume-averaged particle size distribution (PSD) modes such that apacked volume fraction (PVF) of the solids mixture is greater than 0.75,preferably greater than 0.80; a solids volume fraction (SVF) of theslurry less than the PVF of the solids mixture; wherein the first PSDmode is at least three times larger than the second PSD mode, the secondPSD mode is larger than the third PSD mode, and the third PSD mode islarger than the fourth PSD mode, and wherein at least one of the secondand third PSD modes is less than 3 times larger than the respectivethird or fourth PSD mode.209. The slurry of embodiment 208, wherein the solids mixture furthercomprises a fifth PSD mode, wherein the fourth PSD mode is larger thanthe fifth PSD mode and preferably less than 3 times larger than thefifth PSD mode.210. The slurry of embodiment 208, wherein the first PSD mode is from 3to 10 times larger than the second PSD mode (preferably about 5 to about7, more preferably about 5.4 to about 6.9, especially about 5.6 to about6.6 times larger than the second PSD mode), the second PSD mode is from1.5 to 4 times larger than the third PSD mode (preferably from about 2to about 2.4 times larger than the third PSD mode), and the third PSDmode is at least 1.25 times larger than the fourth PSD mode.211. The slurry of embodiment 210, wherein the solids mixture furthercomprises a fifth PSD mode, wherein the fourth PSD mode is at least 1.1times larger than the fifth PSD mode.212. The slurry of any one of embodiments 208 to 211, wherein the firstPSD mode is from about 422 microns up to about 853 microns (20/40 mesh),the second PSD mode is from about 60 microns up to about 180 microns(preferably from about 100 microns up to about 150 microns), the thirdPSD mode is from about 25 microns up to about 70 microns (preferablyfrom about 40 microns up to about 60 microns), and the fourth PSD modeis from about 1 micron up to about 40 microns.213. The slurry of embodiment 212, wherein the solids mixture furthercomprises a fifth PSD mode smaller than the fourth PSD mode, wherein thefifth PSD mode is from about 1 micron up to about 25 microns.214. The slurry of any one of embodiments 208 to 213, wherein the solidsmixture further comprises a fifth PSD mode smaller than the fourth PSDmode, wherein the fifth PSD mode is at least 1 micron and the first PSDmode is from about 422 microns (40 mesh) up to about 853 microns (20mesh).215. The slurry of any one of embodiments 208 to 214, wherein the secondPSD mode comprises a total SVF from 5 to 30 percent (preferably from 10to 20 percent, more preferably from 10 to 15 percent), the third PSDmode comprises a total SVF from 3 to 20 percent (preferably from 3 to 10percent), and the fourth PSD mode comprises a total SVF from 5 to 40percent (preferably from 10 to 30 percent), based on a total SVF of thefirst PSD mode.216. The slurry of embodiment 215, wherein the solids mixture furthercomprises a fifth PSD mode smaller than the fourth PSD mode, wherein thefifth PSD mode comprises a total SVF from 1 to 40 percent, based on atotal SVF of the first PSD mode.217. The slurry of any one of embodiments 208 to 216, wherein the secondPSD mode comprises a total SVF from 5 to 30, preferably 10 to 20,percent of a total SVF of the first PSD mode; the third PSD modecomprises a total SVF from 10 to 100, preferably 30 to 60, percent ofthe total SVF of the second PSD mode; and the fourth PSD mode comprisesa total SVF from 10 to 500, preferably 100 to 400, percent of the totalSVF of the third PSD mode.218. The slurry of embodiment 217, wherein the solids mixture furthercomprises a fifth PSD mode, wherein the fifth PSD mode comprises a totalSVF from 20 to 100, preferably 30 to 80, percent of the total SVF of thefourth PSD mode.219. The slurry of any one of embodiments 208 to 218, wherein the firstPSD mode comprises a total SVF from 60 to 80 percent of the total SVF ofthe solids mixture.220. The slurry of embodiment 208, wherein the first PSD mode is between20 and 40 mesh (422-853 μm), the second PSD mode is from about 100 μm toabout 280 μm and, the third PSD mode is from about 15 μm to 60 μm, andthe fourth PSD mode is from about 1 μm to 25 μm.221. The slurry of embodiment 220, further comprising a fifth PSD modewherein the fourth PSD mode is larger than the fifth PSD mode.222. The slurry of any one of embodiments 208 to 221, wherein the slurryfurther comprises a fluid loss agent to inhibit leak-off from theslurry.223. The slurry of embodiment 222, wherein the fluid loss agent isselected from the group consisting of: latex dispersions, water solublepolymers, submicron particulates, particulates with an aspect ratiohigher than 6, and combinations thereof.224. The slurry of embodiment 222 or 223, wherein the fluid loss agentcomprises crosslinked polyvinyl alcohol microgel.225. The slurry of any one of embodiments 222 to 224, wherein the fluidloss agent further comprises AMPS.226. The slurry of any one of embodiments 208 to 225, wherein the solidsmixture comprises a PVF of at least 0.85, 0.90, 0.95, 0.96, 0.97, 0.98or 0.99.227. The slurry of any one of embodiments 208 to 226, wherein at leastone of the second, third or fourth PSD modes comprises a degradablematerial.228. The slurry of embodiment 227, wherein the solids mixture comprisesa reactive material.229. The slurry of any one of embodiments 208 to 226, wherein the solidsmixture further comprises a fifth PSD mode, wherein at least one of thesecond, third, fourth or fifth PSD modes comprises a degradablematerial.230. The slurry of embodiment 229, wherein the solids mixture comprisesa reactive material.231. A method, comprising: combining a solids mixture and a carrierfluid to form the slurry of any one of embodiments 208 to 230; andpositioning a screen in a wellbore and circulating the slurry throughthe wellbore in any order such that the solids mixture is depositedbetween the screen and the wellbore.232. The method of embodiment 231, wherein the slurry is circulated in ahorizontal portion of the wellbore from toe to heel.233. The method of any one of embodiments 231 to 232, wherein the slurryis circulated in the wellbore at a pressure less than the fracturepressure.234. The method of any one of embodiments 231 to 233, wherein the slurryis circulated in the wellbore at a rate of less than 800 L/min (5 BPM).235. The method of claim any one of embodiments 231 to 234, wherein theslurry is circulated in the wellbore through a washpipe, wherein ascreen-wellbore annulus has a radial thickness relatively less than aradial thickness of a washpipe-screen annulus.236. The method of any one of embodiments 231 to 256, wherein the slurryis circulated in a horizontal portion of the wellbore from toe to heel.237. The method of any one of embodiments 231 to 257, wherein the first,second, third, fourth and any other particulates in the slurry areformed into a pack in an annulus between the screen and the wellbore.238. The method of embodiment 258, further comprising converting thepack into a permeable gravel pack comprising the first amount ofparticulates.239. A system, comprising: a well bore in fluid communication with asubterranean formation; a gravel packing slurry comprising the slurry ofany one of embodiments 208 to 230; a pump to circulate the slurry in thewellbore and a workstring to position a screen in the wellbore in eitherorder to deposit the slurry in one or both of a fracture in theformation and an annulus between the screen and the formation; and meansfor converting the deposited slurry to a gravel pack.240. The system of embodiments 239, further comprising a washpipe tocirculate the slurry through the screen, wherein a screen-wellboreannulus has a radial thickness relatively less than a radial thicknessof a washpipe-screen annulus.241. A system, comprising: a well bore in fluid communication with asubterranean formation; a gravel packing slurry comprising a carrierfluid and a solids mixture, wherein the solids mixture comprises aplurality of volume-averaged particle size distribution (PSD) modes suchthat a packed volume fraction (PVF) exceeds 0.75, preferably exceeds0.8, wherein the solids mixture comprises at least a proppant PSD mode,a fines PSD mode, and one or more intermediate PSD modes selected fromthe group consisting of: PSD modes from 2 to 60 times smaller than theproppant PSD mode, PSD modes from 1.1 to 60 times larger than the finesPSD mode, and combinations thereof, wherein any two of the proppant,intermediate and fines PSD modes have a size ratio less than 3; and apump to circulate the slurry in the wellbore to deposit the solidsmixture and form a proppant pack in one or both of a fracture in theformation and an annulus between a screen and the formation.242. The system of embodiment 241, wherein the intermediate PSD modesinclude a relatively larger intermediate PSD mode and a relativelysmaller intermediate PSD mode, preferably wherein the largerintermediate PSD mode is from 2 to 15 times smaller than the proppantPSD mode and from 1.25 to 15 times larger than the smaller intermediatePSD mode, and wherein the smaller intermediate mode is from 1.1 to 15times larger than the fines PSD mode.243. The system of embodiment 241, further comprising a middleintermediate PSD mode from 1.5 to 4 times smaller than the largerintermediate PSD mode and 1.25 to 2.5 times larger than the smaller PSDmode.244. The system of embodiment 242 or 243, wherein at least oneintermediate PSD mode is degradable, preferably the relatively largerPSD mode.245. A method, comprising: combining a carrier fluid and a solidsmixture to form a slurry, wherein the solids mixture comprises aplurality of volume-averaged particle size distribution (PSD) modes suchthat a packed volume fraction (PVF) exceeds 0.75, preferably exceeds0.8, wherein the solids mixture comprises at least a proppant PSD mode,a fines PSD mode, and one or more intermediate PSD modes selected fromthe group consisting of: PSD modes from 2 to 60 times smaller than theproppant PSD mode, PSD modes from 1.1 to 60 times larger than the finesPSD mode, and combinations thereof, wherein any two of the proppant,intermediate and fines PSD modes have a size ratio less than 3; andcirculating the slurry through a wellbore to form a proppant pack fromdepositing the solids mixture in one or both of a fracture in aformation and an annulus between a screen and the wellbore.246. The method of embodiment 245, wherein the intermediate PSD modesinclude a relatively larger intermediate PSD mode and a relativelysmaller intermediate PSD mode, preferably wherein the largerintermediate PSD mode is from 2 to 15 times smaller than the proppantPSD mode and from 1.25 to 15 times larger than the smaller intermediatePSD mode, and wherein the smaller intermediate mode is from 1.1 to 15times larger than the fines PSD mode.247. The method of embodiment 246, further comprising a middleintermediate PSD mode from 1.5 to 4 times smaller than the largerintermediate PSD mode and 1.25 to 2.5 times larger than the smaller PSDmode.248. The method of embodiment 246 or 247, wherein at least oneintermediate PSD mode is degradable, preferably the relatively largerPSD mode.

EXAMPLES Example 1

A 1 g sample of Al(OH)₃ was added to 20 ml deionized (DI) water. Themixture pH was measured to be 7.7. The particles of Al(OH)₃ wereinsoluble in the DI water at this pH and the mixture was a milky whiteslurry. The pH of the solution was raised to 11.8 by adding 1.5 ml of 50wt % NaOH and the Al(OH)₃ was dissolved, yielding a clear solution.

Example 2

A 1 g sample of Al(OH)₃ was added to 20 ml DI water to form a cloudyslurry as in Example 1. The mixture pH was measured to be 7.2. Themixture pH was decreased by adding 9 ml of 15 wt % HCl. After 18 hours,the Al(OH)₃ dissolved completely and the resulting solution was clear.

Example 3

A slurry containing sand and salt particles was made using saturatedsodium chloride solution (density=1.2 g/mL (10 ppg)) as a carrier fluid.The volume fraction and size of the salt particles were as shown inTable 1 below.

TABLE 1 Volume Fractions in Saturated Brine Slurry Volume Component(mean PSD) fraction Total Sand 49% 443.8 g NaCl crystals (115 microns)8% 59.4 g NaCl crystals (5 micron) 16% 118.8 g NaCl Brine (1.2 g/mL (10ppg)) 27% 90 ml

The slurry was stable and when it was brought into contact with freshwater, the salt particles in the slurry dissolved leaving a porous sandpack.

Example 4

Fines flowback was investigated using an experimental setup consistingof a 51 mm (2-in.) long gravel pack containing 20% fines by volume ofthe gravel in a 25 mm (1-in.) inside diameter tube embedded betweenclean gravel packs without any fines on both sides. The clean gravelpacks served to distribute the flow and to eliminate the end effects atthe entry and exit. A displacement fluid was injected at 5 mL/min or 15mL/min for 30 min and the mass of fines remaining in the pack wasmeasured at the end of the run. The displacement fluid was 2 wt %aqueous KCl unless specified otherwise. The gravel was 20/40 mesh (620microns) or 16/20 mesh (1015 microns) CARBOLITE proppant. The fines were2 micron calcium carbonate. The results are presented in Table 2 below.

TABLE 2 CaCO3 cleanup as a function of gravel size and flow rate (nodispersant) Flow back rate, Gravel Gravel Initial Final Cleanup, ml/minFines Size mass, g fines, g fines, g % 5 CaCO3 20/40 29.36 6.66 6.46 3.0(2 μm) 16/20 33.66 7.59 6.95 8.4 15 CaCO3 20/40 34.16 7.93 6.5 18.0 (2μm) 16/20 34.16 6.96 6.25 10.2

These results showed that the calcium carbonate fines did not easilyflow out of the gravel pack. Next, the flow back tests were repeatedunder different conditions as shown in Table 3 below.

TABLE 3 CaCO₃ cleanup by flow back Gravel CaCO₃ CaCO₃ Mix Flow back Run(620 (125 (2 μm), fluid (10 Displacing Dispersant, rate, Time, Cleanup,No. μm), g μm), g g mL) fluid ml ml/min min % 4-1 50 12.5 DI 2% KCl 0 530 13 4-2 50 12.5 DI 2% KCl 0.1 5 30 98 4-3 50 12.5 2% KCl 2% KCl 0.1 530 41 4-4 50 12.5 2% KCl 2% KCl 0.4 5 30 99 4-5 50 12.5 2% 2% KCl 0.1 530 73 TMAC 4-6 50 6 12.5 DI 2% KCl 0.1 5 30 44 4-7 50 24.6 DI 2% KCl 0.25 30 72 Notes: DI = deionized water TMAC = tetramethylammonium chlorideDispersant = polynaphthalene sulfonate

Runs 4-1 and 4-2 showed that the addition of a small amount (1%) ofdispersant, polynaphthalene sulfonate, increases the fines flow backfrom 13% to 98%. In these runs the fines were mixed with gravel usingdeionized (DI) water as a carrier. In Run 4-3, when the slurry was madeusing 2% KCl, the clean up reduced to 41%. However, increasing theconcentration of dispersant with the 2% KCl carrier fluid in Run 4-4,the cleanup increased from 41% to 99%. Similar results were observed inRun 4-5 when the slurry was made with 2% tetramethyl ammonium chloride(TMAC).

In Run 4-6, the conditions of Run 4-2 were repeated except that thegravel pack additionally included 6 g of 125 micron calcium carbonate.Fines removal using the same amount of dispersant was not as rapid butwas still much improved over the no dispersant case, Run 4-1, suggestingthat additional dispersant would obtain comparable cleanup with andwithout the presence of the intermediate PSD mode. In Run 4-7, theamounts of calcium carbonate fines and dispersant were each doubled, andthe fines cleanup was only slightly reduced relative to Run 4-2, butagain much improved relative to Run 4-1 without dispersant. The data inTable 3 thus demonstrate that flow back of the calcium carbonate finescan be facilitated by the presence of a relatively small amount ofdispersant.

Example 5

Flow back tests similar to Example 4 were then run using 2-micron silicafines, with the conditions and results shown below in Table 4.

TABLE 4 SiO₂ cleanup by flow back Gravel SiO₂ SiO₂ Mix Flow back Run(620 (150 (2 μm), fluid (10 Displacing Dispersant, rate, Time, Cleanup,No. μm), g μm), g g mL) fluid ml ml/min min % 5-1 50 12.5 DI 2% KCl 0 530 8 5-2 50 12.5 DI 2% KCl 0.1 5 30 70 5-3 50 12.5 2% 2% KCl 0.1 5 30 18TMAC 5-4 50 12.5 2% 2% KCl 0.1 5 30 17 TMAC 5-5 50 12.5 2% 2% KCl 0.2 530 23 TMAC 5-6 50 12.5 2% 2% KCl 0.6 5 30 72 TMAC 5-7 50 6 12.5 DI 2%KCl 0.1 5 30 72 5-8 50 12.5 DI 2% KCl 0.2 1 105 83 Notes: DI = deionizedwater TMAC = tetramethylammonium chloride Dispersant = polynaphthalenesulfonate

Runs 5-1 and 5-2, with and without dispersant, show that the flow backresults can be significantly improved by dispersing the SiO₂ fines usingpolynaphthalene sulfonate. Similar to the calcium carbonate fines inExample 4, when the gravel pack was prepared using 2% TMAC in Runs 5-3to 5-6, it was observed that the flow back results could be improved byincreasing the concentration of dispersant relative to the fines.

In Run 5-7, where the gravel pack included an intermediate PSD mode of150-micron silica, the flow back of the fine silica particles was notaffected by the presence of the medium particles. Theoretically, thepore space of 150-micron diameter spheres is 25 microns, which shouldnot restrict dispersed 2-micron particles.

Run 5-8 with displacement fluid at 1 ml/min showed that although theflow back of fines occurred at a slower rate, 83% cleanup was obtainedafter 105 min.

Example 6

Flow back tests similar to Examples 4 and 5 were then run using 5-micronsodium chloride salt fines in saturated NaCl brine (1.2 g/mL (10lb/gal)), with the conditions and results shown below in Table 5.

TABLE 5 NaCl cleanup by flow back Gravel NaCl Mix Displac- Flow backClean- Run (620 (5 fluid ing rate, Time, up, No. μm), g μm), g (10 mL)fluid ml/min min % 6-1 50 10.18 NaCl NaCl 5 30 68 brine brine 6-2 5019.6 NaCl NaCl 5 30 41 brine brine

Saturated brine was used for the slurry and displacement to avoiddissolution of the fines in these runs, although in practice anyundersaturation of the displacement fluid enhances fines removal bydissolving the fines. Although as a percentage the fines removal wasmore rapid in Run 6-1 using 10.18 g NaCl in the gravel pack than in Run6-2, the gross total fines removed was faster in Run 6-2 with more finesin the gravel pack; and fines cleanup is essentially complete in Run 6-2if the flow back is extended to 72 hours.

Example 7

The use of a spacer to inhibit leak-off into a screen using a screenstab-in technique was investigated. In Run 7-1, a 0.3 wt % guar solutionwas placed in a beaker, and a cylindrical screen with a 5 gauge screenelement and a length exceeding the height of the beaker was insertedinto the solution in a vertical orientation. The guar solutionimmediately filled up the interior of the screen and the liquid level inthe annulus between the screen and the wall of the beaker was unchanged.In Run 7-2, the experiment was repeated with the addition of 0.9 wt %polyglycolic acid (PGA) having a mean particle size of 150 microns(d50=150 μm) in the guar solution. The liquid level in the screen-beakerannulus increased when the screen was inserted, and even after 1.5 hoursonly a small volume of the spacer had leaked into the screen.

In Run 7-3, the experiment was repeated using a trimodal slurry havingthe composition set out in Table 6, without using any spacer fluid.

TABLE 6 Slurry composition for Runs 7-3 and 7-4 Particle Component Size(μm) Volume (mL) Weight (g) Ottawa sand d50 = 600 335 888 Silica d50 =30  56.6 150 Silica d50 = 3  109.4 290 DI Water — 190 190

The screen was inserted into the slurry and moved up and down in areciprocating motion in the slurry. After three repetitions, the slurrydehydrated due to leak-off into the screen and the screen became stuckin the solids mixture.

In Run 7-4, the experiment was repeated using the slurry of Table 6 inthe bottom of the beaker and the spacer fluid of Run 7-2 floating on topof the slurry. The screen was inserted into the slurry by passing itthrough the spacer fluid. After 15 repetitions of reciprocating motion,the slurry remained fluid, the screen could still be moved in the slurryand very little fluid leaked into the screen from the slurry. These datashow that contacting the screen with a spacer fluid containing adegradable bridging particle in advance of the multimodal slurry contactwas effective in inhibiting fluid leak-off from the multimodal slurry tomaintain flowability of the slurry.

Example 8

The design of a high-solids slurry to inhibit leak-off into a screen byforming a bridge on the screen was investigated. Two trimodal slurrieswere prepared using the compositions in Table 7.

TABLE 7 Slurry composition for Runs 8-1 and 8-2 Component Particle Size(d50, μm) Run 8-1 (g) Run 8-2 (g) Sand 600 888 Sand 280 888 Silica 30150 150 Silica 3 290 290 DI Water — 190 190

A 5 gauge closed-end screen was inserted into the two slurries and wasmoved up and down in a reciprocating motion in the slurries, in the samemanner as in Example 7. In the slurry of Run 8-1 the screen was stuckafter 3 repetitions, whereas in Run 8-2 the screen was mobile in theslurry even after 10 repetitions. In Run 8-2, small bridges of particleswere observed on the screen during the reciprocating motion. Thisexample shows that the slurry of Run 8-2 controls leak-off into thescreen, thereby maintaining its fluidity during the screen stab-inprocess, or during the slurry placement in the screen-first process.

Example 9

The design of a four-particle high-solids slurry using standard gravelsizes (20/40 mesh) to inhibit leak-off into a screen by forming a bridgeon the screen was investigated. In an initial testing protocol, asyringe fluid loss experiment was conducted by loading 30 mL of slurryinto a 60 mL syringe fitted with a 60 mesh (250 μm openings) screen atthe exit. The plunger was displaced up to the 50 mL mark on the syringeand the spurt was measured on a balance, after the spurt measurement,the syringe was turned upside down and the thickness of the filter cakecollected on the screen was measured. Multimodal slurries were preparedusing the compositions in Table 8. The spurt and filter cake thicknessof three slurries made with 20/40 CARBOLITE as a coarse particle areshown in Table 8 for Runs 9-1, 9-2 and 9-3. The filter cake thicknesswas reported as volume occupied in the 60 mL syringe. Since the initialvolume of slurry in the syringe was 30 mL, a filter cake thickness of 30mL indicated that the slurry lost all its liquid content and what wasleft in the syringe was essentially a solid plug. The results in Table 8show that varying the size of the medium particle from 32 μm to 125 μmto 200 μm did not help in controlling leak-off. In all three slurries ofRuns 9-1, 9-2 and 9-3, the liquid required to keep the slurry flowablewas lost in the spurt stage leaving behind a thick filter cake.

TABLE 8 Slurry Composition and Spurt Results for Runs 9-1 to 9-6 Run RunRun Run Run Run 9-1 9-2 9-3 9-4 9-5 9-6 Component CARBOLITE (20/40, 100100 100 50 50 50 620 μm), g CARBOLITE (40/70, 16 300 μm), g Silica (200μm), g 6 6 CaCO3 (125 μm), g 16 Silica (32 μm), g 16 8 15 Silica (3 μm),g 33 16 24 16 CaCO3 (2 μm), g 33 33 DI Water, g 24 22 22 10 10 10.4Polynaphthalene 0.1 0.1 sulfonate, ml Spurt Results Spurt, g 6.00 10 100.34 9.0 7.4 Cake, mL 30 30 30 5 30 30

After performing leak-off experiments with several combinations oftrimodal particles it was found that an additional particle in the sizerange of 200 μm was able to stop the flow of 32 μm and 2 μm particlesout of the 20/40 mesh gravel pack. The leak-off results in Run 9-4 withthe four-particle system including an additional 200 μm particle reducedthe spurt and filter cake thickness significantly. Runs 9-5 and 9-6omitted either the 32 μm particles or the 200 μm particles, and thespurt and filter cake thickness increased significantly, showing thatthe presence of both 200 μm and 32 μm particles retained the fines andthe liquid content in the slurry. These results suggest that the threelower sizes form an effective bridge in the 20/40 CARBOLITE pack wherethe 200 μm particles occupy the void space of 20/40 gravel, the 32 μmparticles occupy the void space of the 200 μm particles and the 3 μmparticles occupy the void space of 32 μm particles.

In additional Runs 9-7 to 9-12, the amounts of the 200 μm particles and32 μm particles were varied and the results are listed in Table 9.

TABLE 9 Slurry Composition and Spurt Results for Runs 9-6 to 9-12 RunRun Run Run Run Run Run 9-6 9-7 9-8 9-9 9-10 9-11 9-12 ComponentCARBOLITE (20/40, 50 50 50 50 50 50 50 620 μm), g Silica (200 μm), g 610 14 2 6 6 6 Silica (32 μm), g 8 8 8 8 12 15 4 Silica (3 μm), g 16 1616 16 16 16 16 DI Water, g 10 10 10.5 9.5 10 10 10 Spurt Results Spurt,g 0.34 0.16 0.04 1.64 0.19 0.01 0.64 Cake, mL 5 5 5 20 5 3 10

These data indicate that the spurt and filter cake increase as theproportion of either 200 μm or 32 μm particles was reduced over theconcentrations evaluated, and that the proportions of each particle canbe adjusted to optimize (minimize) spurt and filter cake and maintainhydration and flowability of the slurry during placement of the slurryand/or screen.

Example 10

The ability of the four-particle high-solids slurry of Run 9-11, usingstandard gravel size (20/40 mesh) and having the solids compositionlisted in Table 10 plus a fluid loss additive, to inhibit leak-off intoa screen under high differential pressure conditions was investigated.These experiments were conducted in a commercial high temperature, highpressure (HTHP) fluid loss cell by placing a 12 gauge screen coupon atone end of the cell and loading the slurry on top of the screen. Theleak-off tests were conducted by applying 3.45 MPa (500 psi)differential pressure with N2 gas for a period of 30 minutes at roomtemperature (24 C).

TABLE 10 Slurry Solids Composition for High Pressure Screen Leak-offSolid Volume, % of Component Weight, g Volume, mL Total Solids CARBOLITE200 73.8 57 (20/40, 620 μm), g Silica (200 μm), g 24 9.1 7 Silica (32μm), g 60 22.6 17 Silica (3 μm), g 64 24.2 19

Run 10-1 used a slurry prepared with crosslinked polyvinyl alcohol(PVOH) as a fluid loss additive, in the form of a 4 wt % microgelaqueous suspension in which the water-swollen microgel particles have asize of around 100 nm. In Run 10-2 a 10 wt % active solution of highmolecular weight acrylamido-methyl-propane sulfonate polymer (AMPS) wasadded as a polymeric fluid loss additive in addition to the PVOH. Thecompositions of the slurries and the HTHP results are presented in Table11.

TABLE 11 Slurry Composition and High Pressure Screen Leak-off ResultsRun Run Run Run Run Run 10-1 10-2 10-3 10-4 10-5 10-6 Component/Property Solids (Table 348 348 348 348 348 348 10), g 4% PVOH 40 40 2422 16 50 Microgel, mL 10% AMPS, 0 8 0 0 0 0 mL DI Water, mL 52 52 32 5236 28 Solids Volume 0.58 0.56 0.70 0.62 0.72 0.62 Fraction Fluid Loss 4340 43 30 30 64 Agent, vol % of liquid Spurt Results Spurt, g 2.4 3.0 0 00 3.0 15 Minute, g 4.6 5.0 1.6 2.4 1.8 4.4 30 Minute, g 5.6 6.4 2.6 3.83.0 5.0 Filter cake, 7.1 5.6 11.2 15.1 17.6 8.0 mm (in.) (0.28) (0.22)(0.44) (0.59) (0.69) (0.31)

These data show that leak-off can be effectively inhibited even at highdifferential pressure using a four-particle slurry with a fluid lossadditive. At the same fluid loss agent loading, the filter cakethickness can be reduced by reducing the SVF of the slurry. At high SVF,even a small amount of leak-off can transform the slurry to an unmixablestate which results in an inefficient cake build up as the particlepacking is not efficient to control leak-off. When the slurry is welldispersed by reducing SVF, the transformation to unmixable staterequires a larger volume of fluid to leak-off and the packing is alsoefficient resulting in a thin filter cake. Runs 10-1/10-3 and 10-4/10-5show the effect of reducing SVF on filter cake thickness whilemaintaining the relative concentration of fluid loss agent in the fluidphase constant, i.e., filter cake thickness could be reduced bydecreasing the SVF. Runs 10-4/10-6 show that the thickness of the filtercake could also be reduced by increasing the concentration of fluid lossagent in the liquid phase while keeping the SVF constant.

Example 11

The ability of a four-particle high-solids slurry, using standard gravelsize (20/40 mesh) and having the solids composition listed in Table 12plus a latex fluid loss additive, to inhibit leak-off into a screenunder high differential pressure conditions was also investigated usingthe testing equipment and protocol of Example 10.

TABLE 12 Slurry Composition and High Pressure Screen Leak-off Resultswith Latex Fluid Loss Agent Component/Property Run 11 CARBOLITE (20/40,620 μm), g 200 Silica (200 μm), g 24 Silica (32 μm), g 60 Silica (3 μm),g 64 Latex Dispersion, mL 45 10% AMPS, mL 8 DI Water, mL 52 SVF 0.57Fluid Loss Agent, vol % of liquid 50 Spurt Results Spurt, mL 0.6 15Minute, mL 2.2 30 Minute, mL 3.2 Filter cake, mm 4.8

Run 11 showed that latex provides very good fluid loss control andresults in a thin filter cake in a four-particle slurry.

Example 12

The testing equipment and protocol of Example 7 was used to demonstratethe screen stab-in performance of a four-particle slurry system.Trimodal and tetramodal slurries were prepared as listed in Table 13.

TABLE 13 Slurry Compositions and Screen Stab-in ResultsComponent/Property Run 12-1 Run 12-2 Slurry Type Trimodal TetramodalCARBOLITE (20/40, 620 μm), g 1600 1600 Silica (200 μm), g 0 384 Silica(32 μm), g 267 480 Silica (3 μm), g 563 512 4% PVOH Microgel, mL 160 10%AMPS, mL 62 DI Water, mL 300 416 Screen Stab-In Results Number of Stabs26 30 Fluid Entering Screen, mL 150 0

If the slurry leaks into the screen as it is stabbed into the slurry,the slurry loses its flow properties and the screen becomes stuck ordifficult to move in the slurry during reciprocation. After 26 stabswith the trimodal slurry in Run 12-1, a significant amount of fluid hadentered the screen, i.e. 50% of the total liquid volume in the slurry.The slurry outside the screen was dehydrated and had lost its flowproperties at the end of the experiment. With the tetramodal slurry andfluid loss agent in Run 12-2, after 30 stabs there was no fluid that hadleaked into the screen at the end of the experiment. The tetramodalslurry had entirely stopped leak-off into the screen.

Example 13

In this example, the effects of varying the size and concentration ofthe smaller particles in a 4-mode PSD system were investigated. A seriesof syringe fluid loss tests similar to Example 9 were performed wherethe particle size and concentration of the second particle were varied.In these tests, the first particle was 20/40 CARBOLITE proppant (averagediameter 770 μm), and the other particles were made of silica. The sizeand concentration of the second particle were varied, the third particlehad an average diameter of 32 μm and the fourth particle had an averagediameter of 3 μm. A dry blend was made using the four particles bymixing 50 g CARBOLITE, x g of the second particle, 5 g of the thirdparticle and 10 g of the fourth particle, where x was 5.5 g, 7 g, 9 g or12 g. The dry blend was made into slurry by adding 10.5 ml of DI water.Table 14 lists the fluid loss observed in the syringe tests for thedifferent slurries.

TABLE 14 Slurry Composition and Syringe Fluid Loss Data for Runs 13-1 to13-4 (Second Particle Size and Concentration Varied) Second Particle Run13-1 Run 13-2 Run 13-3 Run 13-4 Size (P1/P2/P3/P4 = 770/x/32/3, μm)Concentration, g (P1/P2/P3/P4) Size Range, Average Size, 50/5.5/5/1050/7/5/10 50/9/5/10 50/12/5/10 Mesh μm μm LEAK-OFF (mL) −50/+60 250-297274 ND ND 5.90 ND −60/+70 210-250 230 ND ND 5.38 3.1  −70/+100 149-210180 4.32 2.13 1.92 0.72 −100/+140 105-149 127 1.14 0.42 0.72 0.26−140/+170  88-105 96.5 1.68 0.60 0.31 0.2 −170/+200 74-88 81 4.65 4.800.70 0.3 −200/+230 63-74 68.5 ND 6.35 0.65 0.4 −230/+270 53-63 58 ND ND3.28 0.57 −270/+400 37-53 45 ND ND 5.50 3.35 ND = Not Determined

The data are plotted in FIG. 23 as a function of the second particlesize. As illustrated in FIG. 23, high concentrations of the secondparticle relative to the first particle can allow a broader range of theaverage size of the second particle to be used to reduce leak-off.However, a carefully selected second particle size can allow lowerconcentrations of the second particle to be used, potentiallyfacilitating clean up or removal of the smaller particles to convert thepacked particles from the slurry into a porous, permeable gravel/orproppant pack. For example, at 12 g of the second particle per 50 g20/40 CARBOLITE first particles, an average second particle sizeanywhere between 60 μm and 180 μm effectively bridged the gap betweenthe 20/40 CARBOLITE particles leading to low leak-off. As theconcentration of the second particle was reduced to 5.5 g, however, onlysecond particles in the average size range between 100 μm and 150 μmcontrolled leak-off, with an optimum particle size of about 127 μm+/−10or 15 μm. This example shows that the ratio of the average sizes of thefirst to second particle in this example should be within the range ofabout 770/(127+15)˜5.4 to about 770/(127−15)˜6.9, preferably from about5.6 to about 6.6, or ideally about 770/127˜6.06.

Another series of tests were then run using the 127 μm second particlewhile varying the size of the third particle as shown in Table 15 below.

TABLE 15 Slurry Composition and Syringe Fluid Loss Data for Run 13-5(Third Particle Size Varied) Third Particle Run 13-5 Size (P1/P2/P3/P4 =770/127/x/3, μm) Concentration, g (P1/P2/P3/P4) Size Average Size,50/7/3/10 Mesh Range, μm μm LEAK-OFF (mL) −140/+170  88-105 96.5 7.78−200/+230 63-74 68.5 1.3 −230/+270 53-63 58 0.58 −270/+400 37-53 45 0.9727-37 32 1.55 11 7.84

The data are plotted in FIG. 24 as a function of the third particlesize. The plot shows that the lowest leak-off rate at this concentrationwas obtained for the 58 μm third particles, establishing a range of theratio of the second particle average size to that of the third particleof from about 2.0 to about 2.4, ideally about 2.18.

An approximate packing model for the particle size ratios according toone embodiment is seen in FIG. 25, which was obtained using theDescartes circle theorem. For four mutually tangent circles withcurvatures, P₁, P_(n+1), P_(n+2), and P_(n+3), the following equation(1) is applicable:

$\begin{matrix}{{\frac{1}{P_{n}^{2}} + \frac{1}{P_{n + 1}^{2}} + \frac{1}{P_{n + 2}^{2}} + \frac{1}{P_{n + 3}^{2}}} = {\frac{1}{2}\left( {\frac{1}{P_{n}} + \frac{1}{P_{n + 1}} + \frac{1}{P_{n + 2}} + \frac{1}{P_{n + 3}}} \right)^{2}}} & (1)\end{matrix}$where P_(n) is the curvature of circle n, where curvature is taken asthe reciprocal of the radius. For example, when three equally sizedspheres (Size P1=1) are touching each other, the size (diameter) ratioof P1/P2 can be obtained using the above equation to be 6.464˜6.5.Similarly, the other ratios for the particle sizes required to stopleak-off in an embodiment can be estimated as P2/P3 being about 2.5 andP3/P4 being about 1.8, and when a fifth particle is used, P4/P5 is about1.6. As a practical matter it can be difficult to obtain and/or workwith particles having an average size range less than about 10 μm at theaccuracy required, and one embodiment compensates by using a relativelylarge proportion of the fourth particle wherein the fourth particle hasan average size between 10 and 20 μm.

Example 14

In this example the stability of a slurry was qualitatively observed byaging the slurry in a glass bottle under static conditions for 48 h inthe temperature range of 66° C. (150° F.) to 121° C. (250° F.). At theend of 48 h, a pipette was manually inserted into the slurry to gaugethe force required to stab into the slurry. This was a qualitative testand the force required to stab in was assigned a number from 0 to 5 with0 being the worst case (cannot stab in) and 5 being the best case. Afterthe stab-in test, the slurry was poured out of the bottle to check theflow properties and settling at the bottom of the slurry. Theflowability was also assigned a number between 0 and 5, where 0 refersto not flowable and 5 refers to flowable slurry.

In Runs 14-1 to 14-3 a four-particle slurry as shown in Table 16 wasevaluated at 66° C., 93° C. and 121° C. using diutan (0.036 wt %) as aviscosifier in the liquid phase.

TABLE 16 Slurry Compositions and Stability Results with Diutan SlurryStabilizer Component/Property Run 14-1 Run 14-2 Run 14-3 Temperature, C.66 93 121 CARBOLITE (20/40, 620 μm), g 100 100 100 Silica (200 μm), g 1212 12 Silica (32 μm), g 30 30 30 Silica (3 μm), g 32 32 32 DI Water, g23 23 23 Diutan, g 0.008 0.008 0.008 Slurry Stability Results, 64 hStab-In, scale 0-5 5 5 5 Flow, scale 0-5 4 4 4 Settling yes yes yes

After 64 h at temperature, it was easy to stab-in a pipette into theslurry and also to pour the slurry out of the bottle. However, asediment was observed in the bottle.

In Run 14-4, a four-particle slurry as shown in Table 17 was evaluatedat 121 C using nanometer sized γ-alumina (40 nm, obtained from InfarmatAdvanced Materials) as a slurry stabilizer.

TABLE 17 Slurry Composition and Stability Result with γ-Alumina SlurryStabilizer Component/Property Run 14-4 Temperature, C. 121 CARBOLITE(20/40, 620 μm), g 100 Silica (200 μm), g 12 Silica (32 μm), g 30 Silica(3 μm), g 32 DI Water, g 26 γ-Al2O3, g 0.008 Polynaphthalene sulfonate,ml 0.17 Slurry Stability Results, 86 h Stab-In, scale 0-5 5 Flow, scale0-5 5 Free water No Settling Little

The stab-in, flow and free water results showed that the stability ofthe slurry was much better than that formulated with diutan. A uniqueproperty of slurries formulated with γ-alumina is that they do not havea layer of free water at the end of the experiment.

In Run 14-5, a four-particle slurry as shown in Table 18 was evaluatedat 121° C. using gellan particles at 0.2 wt % and diutan at 0.036 wt %.At room temperature, the gellan particles dispersed easily in water butdid not increase the viscosity of the mixture. At temperatures above 90°C., the gellan particles hydrate, increasing the viscosity of thesolution. This is a very useful property in one embodiment of theinvention because the particles can be added to the slurry at thesurface without increasing the viscosity. After the slurry is placeddownhole, the decrease in viscosity of liquid phase due to temperaturecan be compensated by the increase in viscosity due to hydration ofgellan particles.

TABLE 18 Slurry Composition and Stability Result with Gellan/DiutanSlurry Stabilizer Component/Property Run 14-5 Temperature, C. 121CARBOLITE (20/40, 620 μm), g 100 Silica (200 μm), g 12 Silica (32 μm), g30 Silica (3 μm), g 42 DI Water, g 28 Diutan, g 0.01 Gellan gum, g 0.06Slurry Stability Results, 86 h Stab-In, scale 0-5 5 Flow, scale 0-5 5Free water Yes Settling No

The results in Table 18 showed that the slurry was stable and did notshow settling at the end of the experiment.

In Runs 14-6, 14-7 and 14-8, the gellan/diutan, four-particle slurry ofTable 18 was evaluated at different temperatures after 48 h as shown inTable 17.

TABLE 19 Stability Result with Gellan/Diutan Slurry Stabilizer SlurryStability Results, 48 h Run 14-6 Run 14-7 Run 14-8 Temperature, ° C. 6693 121 Stab-In, scale 0-5 5 5 5 Flow, scale 0-5 5 5 5 Free water No NoNo Settling No No No

The results in Table 19 showed that the slurry was stable when the fluidphase is viscosified at high temperature with gellan gum.

In Run 14-9, a four-particle slurry as shown in Table 20 was evaluatedat 121° C. using polylactic acid (PLA) flakes to improve stability. Thefluid phase of the slurry was not viscosified with diutan. The averagesize of the PLA flakes was around 1 mm.

TABLE 20 Slurry Composition and Stability Result with PLA SlurryStabilizer Component/Property Run 14-9 Temperature, ° C. 121 CARBOLITE(20/40, 620 μm), g 100 Silica (200 μm), g 12 Silica (32 μm), g 30 Silica(3 μm), g 32 DI Water, g 26 PLA Flakes, g 2 Slurry Stability Results, 86h Stab-In, scale 0-5 5 Flow, scale 0-5 5 Free water Yes Settling Little

The results in Table 20 showed that the addition of PLA flakes improvedthe stab-in, flow and settling properties of the slurry when compared tothe stability results of the slurry formulated with diutan as shown inTable 16.

While the invention has been illustrated and described in detail in thedrawings and foregoing description, the same is to be considered asillustrative and not restrictive in character, it being understood thatonly some embodiments have been shown and described and that all changesand modifications that come within the spirit of the inventions aredesired to be protected. It should be understood that while the use ofwords such as preferable, preferably, preferred, more preferred orexemplary utilized in the description above indicate that the feature sodescribed may be more desirable or characteristic, nonetheless may notbe necessary and embodiments lacking the same may be contemplated aswithin the scope of the invention, the scope being defined by the claimsthat follow. In reading the claims, it is intended that when words suchas “a,” “an,” “at least one,” or “at least one portion” are used thereis no intention to limit the claim to only one item unless specificallystated to the contrary in the claim. When the language “at least aportion” and/or “a portion” is used the item can include a portionand/or the entire item unless specifically stated to the contrary.

The invention claimed is:
 1. A method, comprising: combining a solidsmixture and a carrier fluid to form a slurry, wherein the solids mixturecomprises first, second, third and fourth volume-averaged particle sizedistribution (PSD) modes such that a packed volume fraction (PVF) of thesolids mixture is greater than 0.75, and wherein a solids volumefraction (SVF) of the slurry is less than the PVF of the solids mixture;wherein the first PSD mode is at least three times larger than thesecond PSD mode, the second PSD mode is larger than the third PSD mode,and the third PSD mode is larger than the fourth PSD mode, and whereinat least one of the second and third PSD modes is less than 3 timeslarger than the respective third or fourth PSD mode; and positioning ascreen in a wellbore and circulating the slurry through the wellbore inany order such that the solids mixture is deposited between the screenand the wellbore.
 2. The method of claim 1, wherein the solids mixturefurther comprises a fifth PSD mode, wherein the fourth PSD mode islarger than the fifth PSD mode.
 3. The method of claim 1, wherein thefirst PSD mode is from 3 to 10 times larger than the second PSD mode,the second PSD mode is from 1.5 to 4 times larger than the third PSDmode, and the third PSD mode is at least 1.25 times larger than thefourth PSD mode.
 4. The method of claim 3, wherein the solids mixturefurther comprises a fifth PSD mode, wherein the fourth PSD mode is atleast 1.1 times larger than the fifth PSD mode.
 5. The method of claim1, wherein the first PSD mode is from about 422 microns up to about 853microns (20/40 mesh), the second PSD mode is from about 60 microns up toabout 180 microns, the third PSD mode is from about 25 microns up toabout 70 microns, and the fourth PSD mode is from about 1 micron up toabout 40 microns.
 6. The method of claim 5, wherein the solids mixturefurther comprises a fifth PSD mode smaller than the fourth PSD mode,wherein the fifth PSD mode is from about 1 micron up to about 25microns.
 7. The method of claim 1, wherein the solids mixture furthercomprises a fifth PSD mode smaller than the fourth PSD mode, wherein thefifth PSD mode is at least 1 micron and the first PSD mode is from about422 microns (40 mesh) up to about 853 microns (20 mesh).
 8. The methodof claim 1, wherein the second PSD mode comprises a total SVF from 5 to30 percent, the third PSD mode comprises a total SVF from 3 to 20percent, and the fourth PSD mode comprises a total SVF from 5 to 40percent, based on a total SVF of the first PSD mode.
 9. The method ofclaim 8, wherein the solids mixture further comprises a fifth PSD mode,wherein the fifth PSD mode comprises a total SVF from 1 to 40 percent,based on a total SVF of the first PSD mode.
 10. The method of claim 1,wherein the first PSD mode comprises a total SVF from 60 to 80 percentof the total SVF of the solids mixture.
 11. The method of claim 1,wherein the first PSD mode is between 20 and 40 mesh (422-853 μm), thesecond PSD mode is from about 140 μm to about 280 μm and, the third PSDmode is from about 15 μm to 60 μm, and the fourth PSD mode is from about1 μm to 25 μm.
 12. The method of claim 1, wherein the slurry furthercomprises a fluid loss agent to inhibit leak-off from the slurry. 13.The method of claim 12, wherein the fluid loss agent is selected fromthe group consisting of: latex dispersions, water soluble polymers,submicron particulates, particulates with an aspect ratio higher than 6,and combinations thereof.
 14. The method of claim 12, wherein the fluidloss agent comprises crosslinked polyvinyl alcohol microgel.
 15. Themethod of claim 14, wherein the fluid loss agent further comprises AMPS.16. The method of claim 1, wherein the solids mixture comprises a PVF ofat least 0.95.
 17. The method of claim 1, wherein at least one of thesecond, third or fourth PSD modes comprises a degradable material. 18.The method of claim 17, wherein the solids mixture further comprises areactive material.
 19. The method of claim 1, wherein the slurry iscirculated in a horizontal portion of the wellbore from toe to heel. 20.The method of claim 1, wherein the slurry is circulated in the wellboreat a pressure less than the fracture pressure.
 21. The method of claim1, wherein the slurry is circulated in the wellbore at a rate of lessthan 800 L/min (5 BPM).
 22. The method of claim 1, wherein the slurry iscirculated in the wellbore through a wash pipe, wherein a screen-wellbore annulus has a radial thickness relatively less than a radialthickness of a washpipe-screen annulus.
 23. The method of claim 22,wherein the slurry is circulated in a horizontal portion of the wellborefrom toe to heel.
 24. The method of claim 23, wherein the slurry iscirculated in the wellbore at a pressure less than the fracture pressureat a rate of less than 800 L/min (5 BPM).
 25. The method of claim 1,wherein the first, second, third, and fourth PSD modes and any otherparticulates in the slurry are formed into a pack in an annulus betweenthe screen and the wellbore.
 26. The method of claim 25, furthercomprising converting the pack into a permeable gravel pack comprisingthe first PSD mode.
 27. A system, comprising: a well bore in fluidcommunication with a subterranean formation; a gravel packing slurrycomprising: a solids mixture in a carrier fluid, wherein the solidsmixture comprises first, second, third and fourth volume-averagedparticle size distribution (PSD) modes such that a packed volumefraction (PVF) of the solids mixture is greater than 0.75; a solidsvolume fraction (SVF) of the slurry less than the PVF of the solidsmixture; wherein the first PSD mode is at least three times larger thanthe second PSD mode, the second PSD mode is larger than the third PSDmode, and the third PSD mode is larger than the fourth PSD mode, andwherein at least one of the second and third PSD modes is less than 3times larger than the respective third or fourth PSD mode; a pump tocirculate the slurry in the wellbore and a workstring to position ascreen in the wellbore in either order to deposit the slurry in one orboth of a fracture in the formation and an annulus between the screenand the formation; and means for converting the deposited slurry to agravel pack.
 28. The system of claim 27, wherein the solids mixturefurther comprises a fifth PSD mode, wherein the fourth PSD mode islarger than the fifth PSD mode.
 29. The system of claim 27, wherein thefirst PSD mode is from 3 to 10 times larger than the second PSD mode,the second PSD mode is from 1.5 to 4 times larger than the third PSDmode, and the third PSD mode is at least 1.25 times larger than thefourth PSD mode.
 30. The system of claim 29, wherein the solids mixturefurther comprises a fifth PSD mode, wherein the fourth PSD mode is atleast 1.1 times larger than the fifth PSD mode.
 31. The system of claim27, wherein the first PSD mode is from about 422 microns up to about 853microns (20/40 mesh), the second PSD mode is from about 60 microns up toabout 180 microns, the third PSD mode is from about 25 microns up toabout 70 microns, and the fourth PSD mode is from about 1 micron up toabout 40 microns.
 32. The system of claim 31, wherein the solids mixturefurther comprises a fifth PSD mode smaller than the fourth PSD mode,wherein the fifth PSD mode is from about 1 micron up to about 25microns.
 33. The system of claim 27, wherein the solids mixture furthercomprises a fifth PSD mode smaller than the fourth PSD mode, wherein thefifth PSD mode is at least 1 micron and the first PSD mode is from about422 microns (40 mesh) up to about 853 microns (20 mesh).
 34. The systemof claim 27, wherein the second PSD mode comprises a total SVF from 5 to30 percent, the third PSD mode comprises a total SVF from 3 to 20percent, and the fourth PSD mode comprises a total SVF from 5 to 40percent, based on a total SVF of the first PSD mode.
 35. The system ofclaim 34, wherein the solids mixture further comprises a fifth PSD mode,wherein the fifth PSD mode comprises a total SVF from 1 to 40 percent,based on a total SVF of the first PSD mode.
 36. The system of claim 27,wherein the first PSD mode comprises a total SVF from 60 to 80 percentof the total SVF of the solids mixture.
 37. The system of claim 27,wherein the first PSD mode is between 20 and 40 mesh (422-853 μm), thesecond PSD mode is from about 140 μm to about 280 μm and, the third PSDmode is from about 15 μm to 60 μm, and the fourth PSD mode is from about1 μm to 25 μm.
 38. The system of claim 27, wherein the slurry furthercomprises a fluid loss agent to inhibit leakoff from the slurry.
 39. Thesystem of claim 38, wherein the fluid loss agent is selected from thegroup consisting of: latex dispersions, water soluble polymers,submicron particulates, particulates with an aspect ratio higher than 6,and combinations thereof.
 40. The system of claim 38, wherein the fluidloss agent comprises crosslinked polyvinyl alcohol microgel.
 41. Thesystem of claim 40, wherein the fluid loss agent further comprises AMPS.42. The system of claim 27, wherein the solids mixture comprises a PVFof at least 0.95.
 43. The system of claim 27, wherein at least one ofthe second, third or fourth PSD modes comprises a degradable material.44. The system of claim 43, wherein the solids mixture further comprisesa reactive material.
 45. The system of claim 27, further comprising awashpipe to circulate the slurry through the screen, wherein ascreen-wellbore annulus has a radial thickness relatively less than aradial thickness of a washpipe-screen annulus.